fix(webui,gui): repair dead export button + wire chat clear; prune UI redundancy

WebUI (internal/gateway/ui):
- BUG: the export modal's custom-range button called
  downloadStatsCsvFromForm() which was never defined — clicking it threw a
  ReferenceError and nothing downloaded. Implement it: reads #exp-from /
  #exp-to date inputs and forwards to downloadStatsCsv.
- BUG-adjacent: clearChat() existed but was reachable from no control —
  add a Clear button to the chat composer so conversation reset is actually
  possible (+ cClear i18n zh/en).
- remove byte-identical duplicate html[data-theme=dark] CSS block (15 lines)
- remove 8 dead CSS rules (.keys-grid .m-model-row .scope-add/.scope-box/
  .scope-chips .scr-blocks .tag-warn .twrap) and the never-consumed
  --accent custom property
- remove 3 dead JS functions (activeTab/findSlots/scopeUncomb; lastTab decl kept)
- remove 24 dead i18n keys x zh/en (~55 lines) — legacy of the replaced
  key-scope editor, matching the removed .scope-* styles

GUI (cmd/gui/main.js):
- BUG: stopCore() set app.isQuitting=true and nothing reset it — after using
  tray 'stop core', closing the window quit the whole app instead of hiding
  to tray, and core crash auto-restart stayed disabled. isQuitting now only
  flips in restartCore (scoped) and before-quit.

Verified: go vet/test green; node --check on all three GUI js files and the
WebUI inline script.

internal/gateway/ui/index.html

@@ -28,7 +28,6 @@
         --sh-lg:0 18px 46px rgba(120,90,160,.22);
         --glass:18px;
         --ease-spring:cubic-bezier(.34,1.56,.64,1);
-        --accent:sakura;
       }
       html[data-accent="sakura"]{
         --primary:#FF7FAC; --primary-h:#F33B7C; --primary-50:#FFF0F5; --primary-100:#FFE4E9;
@@ -84,20 +83,6 @@
         --blob1:rgba(168,85,247,.32); --blob2:rgba(34,211,238,.26); --blob3:rgba(139,92,246,.22);
         --line:rgba(168,85,247,.16); --line-strong:rgba(139,92,246,.18);
       }
-      html[data-theme="dark"]{
-        --primary:#f54180; --primary-h:#f871a0; --primary-50:#310413; --primary-100:#610726;
-        --primary-200:#920b3a; --primary-300:#c20e4d; --primary-400:#f31260; --primary-500:#f54180;
-        --secondary:#5E9FBF; --secondary-h:#88C0D0; --secondary-50:#0E2A36; --secondary-200:#2A546A;
-        --danger:#DB3694; --danger-50:#3d1a24; --ok:#4f7cff; --warn:#e0b25c; --info:#6a8ffb;
-        --bg-s1:#14121c; --bg-s2:#1a1824; --bg-s3:#221a28;
-        --card:rgba(34,31,50,.55); --card-solid:#241f38; --card2:rgba(44,39,64,.42);
-        --line:rgba(255,127,172,.16); --line-strong:rgba(200,180,235,.18);
-        --fg:#ece6f5; --muted:#a09db8;
-        --blob1:rgba(255,79,160,.32); --blob2:rgba(100,180,215,.26); --blob3:rgba(219,54,148,.22);
-        --sh-sm:0 1px 2px rgba(0,0,0,.35), inset 0 1px 0 rgba(255,255,255,.05);
-        --sh-md:0 8px 26px rgba(0,0,0,.45);
-        --sh-lg:0 20px 52px rgba(0,0,0,.55);
-      }
       *{box-sizing:border-box}
       html,body{height:100%}
       body{margin:0;color:var(--fg);overflow:hidden;
@@ -187,7 +172,6 @@
       .tag-green{background:var(--primary-50);color:var(--ok)}
       .tag-red{background:var(--danger-50);color:var(--danger)}
       .tag-blue{background:var(--secondary-50);color:var(--secondary-h)}
-      .tag-warn{background:rgba(183,121,31,.14);color:var(--warn)}
       .net-dot{display:inline-block;width:7px;height:7px;border-radius:50%;background:currentColor;margin-right:6px;vertical-align:1px}
       button{background:linear-gradient(135deg,var(--primary),var(--danger));color:#fff;border:0;border-radius:11px;padding:8px 16px;cursor:pointer;
         font:inherit;font-weight:600;transition:all .18s var(--ease-spring)}
@@ -278,7 +262,6 @@
       .filter-line select{width:auto;margin:0;padding:6px 10px}
 
       /* ---- keys tab ---- */
-      .keys-grid{display:flex;flex-direction:column;gap:12px}
       .key-row{display:flex;align-items:center;gap:10px;padding:10px 12px;border:1px solid var(--line);border-radius:12px;background:var(--card);flex-wrap:wrap}
       .key-row .kr-name{font-weight:700;min-width:120px}
       .key-row .kr-key{font-family:'JetBrains Mono',ui-monospace,Consolas,monospace;font-size:12px;color:var(--muted);overflow:hidden;text-overflow:ellipsis;max-width:340px;white-space:nowrap}
@@ -287,14 +270,11 @@
       .tag-role{font-size:11px;padding:3px 10px;border-radius:99px;font-weight:700}
       .tag-role.admin{background:linear-gradient(135deg,var(--primary),var(--danger));color:#fff}
       .tag-role.user{background:var(--secondary-50);color:var(--secondary-h);border:1px solid var(--line)}
-      .scope-box{border-top:1px dashed var(--line);margin-top:8px;padding-top:10px}
-      .scope-chips{display:flex;flex-wrap:wrap;gap:8px;align-items:center;min-height:40px}
       .scope-chip{display:inline-flex;align-items:center;gap:6px;padding:5px 10px;border-radius:99px;background:linear-gradient(135deg,var(--primary),var(--secondary));color:#fff;font-size:12.5px;font-weight:600;cursor:grab;user-select:none}
       .scope-chip[draggable="true"]:active{cursor:grabbing}
       .scope-chip .rm{cursor:pointer;opacity:.75;font-size:13px;line-height:1;padding:0 2px}
       .scope-chip .rm:hover{opacity:1}
       .scope-chip.drag-over{outline:2px dashed #fff;outline-offset:2px}
-      .scope-add{padding:5px 10px;border-radius:99px;border:1px dashed var(--line);background:transparent;color:var(--muted);font-size:12.5px;cursor:pointer}
       .scope-unlim{color:var(--primary-h);font-weight:700;font-size:13px}
       .keys-create{display:grid;grid-template-columns:1fr 2fr 1fr 2fr;gap:10px;align-items:end}
       .keys-create label{font-size:11.5px;color:var(--muted);margin-bottom:4px}
@@ -383,7 +363,6 @@
       #modal-wrap{position:fixed;inset:0;background:rgba(30,20,60,.45);display:none;align-items:flex-start;justify-content:center;overflow:auto;padding:48px 20px;z-index:50;backdrop-filter:blur(3px)}
       #modal-wrap:not(:empty){display:flex}
       #modal-wrap .card{width:100%;max-width:480px;animation:cardIn .28s var(--ease-spring) both}
-      .twrap{overflow-x:auto;-webkit-overflow-scrolling:touch}
 
       /* ---- scratch-style priority canvas (sakura restyle, same classes) ---- */
       .sort-canvas{position:relative;min-height:420px;padding:22px 14px 30px;margin:4px 0 10px;background-color:var(--card2);
@@ -395,7 +374,6 @@
       .scr-lane.scr-top .scr-tier span{opacity:.95}
       .scr-row{flex:1 1 auto;display:flex;align-items:center;padding:2px 18px;border-radius:8px;position:relative;transition:background .18s}
       .scr-row.hover{background:var(--primary-50)}
-      .scr-blocks{display:flex;flex-wrap:wrap;align-items:center;min-width:0}
       .scr-block{position:relative;display:flex;align-items:center;gap:10px;padding:12px 14px 12px 20px;color:#fff;font-weight:700;font-size:13px;user-select:none;margin-right:0;
         border-radius:11px 11px 7px 7px;box-shadow:0 6px 0 rgba(0,0,0,.14),inset 0 2px 0 rgba(255,255,255,.30),inset 0 -5px 0 rgba(0,0,0,.08);transition:opacity .15s}
       .scr-block::before{content:'';position:absolute;left:-7px;top:50%;transform:translateY(-50%);width:7px;height:30px;border-radius:7px 0 0 7px;background:inherit;z-index:2}
@@ -451,7 +429,6 @@
       .scr-block .scr-x{position:absolute;top:-6px;right:-6px;cursor:pointer;font-size:13px;line-height:1;padding:3px 5px;border-radius:50%;
         color:rgba(255,255,255,.9);background:rgba(0,0,0,.22);z-index:3}
       .scr-block .scr-x:hover{background:rgba(219,54,148,.85);color:#fff}
-      .m-model-row{display:flex;gap:8px;align-items:center}
       .m-id{margin:0 0 8px}
       .m-kind{flex:0 0 auto;margin:0 0 8px}
       .donut{position:relative;width:108px;height:108px}
@@ -729,14 +706,12 @@
         zh: {
           tagline: "统一 LLM 网关",
           logout: "退出登录",
-          langTo: "EN",
           navStatus: "状态",
           navChat: "对话",
           navSources: "源",
           navAdapters: "适配器",
           navSort: "优先级",
           navKeys: "密钥",
-          keysTitle: "密钥管理",
           keysHint:
             "管理员密钥可查看与管理全部密钥，并可为每个用户密钥配置可用模型范围；用户密钥只能看到自己。",
           kCreate: "新建密钥",
@@ -747,30 +722,18 @@
           kNote: "备注",
           kCreateBtn: "创建",
           kKey: "密钥",
-          kModels: "可用模型",
-          kCreated: "创建时间",
-          kActions: "操作",
           kCopy: "复制密钥",
           kDel: "删除",
           kNewKey: "新密钥",
           kNewOK: "密钥已创建",
-          kScope: "配置模型范围",
           kScopeTitle:
             "配置模型范围 —— 拖拽排列、下拉添加、×删除、复制/粘贴到其它用户",
-          kScopeHint: "拖拽排序 · 下拉添加 · × 删除 · 复制/粘贴列表",
-          kScopeSel: "选择模型…",
-          kCopyList: "复制列表",
-          kPasteList: "粘贴列表",
           kSaveScope: "保存",
-          kScopeSaved: "模型范围已保存",
-          kScopeEmpty: "全部模型",
-          kScopeAll: "空即不限",
           kMeTitle: "我的密钥",
           kMeRole: "角色",
           kMeModels: "我可用的模型",
           kMeHint: "密钥不可在此新建或删除；需要变更请联系管理员。",
           kEmpty: "暂无其他密钥",
-          kDelSelf: "不能删除当前登录所用密钥",
           kDelConfirm: "确定删除密钥 %s 吗？此后该密钥立即失效。",
           kAll: "不限",
           kBrickH: "点击编辑模型与配额 · 右键更多操作 · 拖动可跨密钥移动",
@@ -805,7 +768,6 @@
           copyCfg: "一键复制配置",
           copyEnv: "复制为环境变量",
           srcTitle: "源状态",
-          srcCount: "共 %d 个",
           tName: "名称",
           tAdapter: "适配器",
           tModels: "模型",
@@ -816,13 +778,12 @@
           offline: "退避 / 不可用",
           adTitle: "已加载适配器",
           tVersion: "版本",
-          chatTitle: "Chat 测试",
           cModel: "模型",
           cMsg: "Enter 发送，Shift+Enter 换行",
           send: "发送",
+          cClear: "清空",
           clear: "清空",
           cThinking: "推理",
-          cImg: "图片",
           cPick: "选择图片",
           cRemoveImg: "移除",
           cWelcome: "开始对话——选择模型，输入消息即可测试上游连接",
@@ -884,20 +845,15 @@
           sortTitle: "拖拽积木配置模型优先级",
           sortHint:
             "每行 = 一个优先级档位，行从上到下优先级递减；同一行的模型并排，视为同优先级。按住积木右侧 ⠿ 把手拖动：拖到行内 = 放入该档位或调整同档顺序，拖到行与行之间的缝隙 = 提升或降低到新档位。生图模型不参与排序。",
-          sortDragGrip: "拖拽前须按住把手",
           sortSave: "保存排序",
           sortReset: "重置",
           sortAdd: "添加档位",
           sortSaved: "排序已保存并热重载",
-          sortNoChange: "无变更",
           sortHintSave: "点击保存排序后生效",
           sortCooling: "冷却",
           sortFail: "失败",
           sortHealthTip: "冷却 / 失败次数 / 偏好分 实时状态",
           sortHealthReset: "链上冷却已复位",
-          sortSource: "源",
-          sortPrio: "优先级 %s",
-          sortEmpty: "该源暂无模型",
           kpiActive: "活跃请求",
           kpiReqs: "总请求",
           kpiOk: "成功率",
@@ -919,7 +875,6 @@
           expKeysCsv: "导出密钥用量",
           exitKeyView: "退出该密钥视图",
           dashStatus: "状态码分布",
-          thCode: "状态码",
           kOther: "其他",
           statusTag:
             "状态码分类统计（含 402 欠费 / 400 schema 错误；两者不计入上游退避但单独计数）",
@@ -945,14 +900,12 @@
         en: {
           tagline: "Unified LLM Gateway",
           logout: "Log out",
-          langTo: "中",
           navStatus: "Status",
           navChat: "Chat",
           navSources: "Sources",
           navAdapters: "Adapters",
           navSort: "Priority",
           navKeys: "Keys",
-          keysTitle: "Key management",
           keysHint:
             "Admin keys can view and manage every key and configure each user key\u0027s allowed models; user keys only see themselves.",
           kCreate: "Create key",
@@ -963,32 +916,19 @@
           kNote: "Note",
           kCreateBtn: "Create",
           kKey: "Key",
-          kModels: "Allowed models",
-          kCreated: "Created",
-          kActions: "Actions",
           kCopy: "Copy key",
           kDel: "Delete",
           kNewKey: "New key — copy & save it now",
           kNewOK: "Key created",
-          kScope: "Model scope",
           kScopeTitle:
             "Model scope — drag to order, add from dropdown, × to remove, copy/paste the list to other users",
-          kScopeHint:
-            "drag to order · add from dropdown · × to remove · copy/paste list",
-          kScopeSel: "Pick a model…",
-          kCopyList: "Copy list",
-          kPasteList: "Paste list",
           kSaveScope: "Save",
-          kScopeSaved: "Model scope saved",
-          kScopeEmpty: "all models",
-          kScopeAll: "empty = unlimited",
           kMeTitle: "My key",
           kMeRole: "Role",
           kMeModels: "Models I can use",
           kMeHint:
             "Keys cannot be created or deleted here; contact an admin to change.",
           kEmpty: "No other keys",
-          kDelSelf: "cannot delete the key you are logged in with",
           kDelConfirm: 'Delete key "%s"? It will stop working immediately.',
           kAll: "All",
           kBrickH:
@@ -1025,7 +965,6 @@
           copyCfg: "Copy config",
           copyEnv: "Copy as env vars",
           srcTitle: "Sources",
-          srcCount: "%d total",
           tName: "Name",
           tAdapter: "Adapter",
           tModels: "Models",
@@ -1036,13 +975,12 @@
           offline: "backoff / down",
           adTitle: "Loaded adapters",
           tVersion: "Version",
-          chatTitle: "Chat",
           cModel: "Model",
           cMsg: "Enter to send, Shift+Enter for newline",
           send: "Send",
+          cClear: "Clear",
           clear: "Clear",
           cThinking: "Thinking",
-          cImg: "Image",
           cPick: "Pick image",
           cRemoveImg: "Remove",
           cWelcome:
@@ -1105,20 +1043,15 @@
           sortTitle: "Drag blocks to set model priority",
           sortHint:
             "Each row = one priority tier, rows go high→low; models on the same row sit side by side and share that priority. Grab the ⠿ handle on the right of a block to drag: drop into a row = join that tier or reorder within it, drop into the gap between rows = move up/down a tier. Image models stay out.",
-          sortDragGrip: "grab the handle to drag",
           sortSave: "Save order",
           sortReset: "Reset",
           sortAdd: "Add slot",
           sortSaved: "Order saved & hot-reloaded",
-          sortNoChange: "No changes",
           sortHintSave: "Click Save for it to take effect",
           sortCooling: "cooling",
           sortFail: "fail",
           sortHealthTip: "live cooldown / failures / preference score",
           sortHealthReset: "chain cooldowns reset",
-          sortSource: "source",
-          sortPrio: "priority %s",
-          sortEmpty: "no models in this source",
           kpiActive: "Active requests",
           kpiReqs: "Requests",
           kpiOk: "Success rate",
@@ -1140,7 +1073,6 @@
           expKeysCsv: "Export key usage",
           exitKeyView: "Exit this key view",
           dashStatus: "Status codes",
-          thCode: "Code",
           kOther: "other",
           statusTag:
             "Per-status aggregates — 402 quota / 400 schema errors are counted here but never back off the provider",
@@ -1191,10 +1123,8 @@
         if (ll) ll.textContent = LANG === "zh" ? "EN" : "中";
         document.documentElement.lang = LANG;
       }
+
       let lastTab = "status";
-      function activeTab() {
-        return lastTab;
-      }
 
       /* ---------- theme & header ---------- */
       /* ---------- chrome: theme / lang / sidebar / breadcrumb ---------- */
@@ -1590,6 +1520,22 @@
         const w = $("#modal-wrap");
         if (w) w.remove();
       }
+      // downloadStatsCsvFromForm reads the custom date range from the export
+      // modal's date inputs and forwards to downloadStatsCsv. (Previously this
+      // was referenced by the modal button but never defined — clicking
+      // "download" did nothing.)
+      function downloadStatsCsvFromForm() {
+        const f = $("#exp-from");
+        const t = $("#exp-to");
+        if (!f || !t) return;
+        // date inputs give YYYY-MM-DD; interpret as local days, end exclusive
+        const from = new Date(f.value + "T00:00:00").getTime();
+        const to = t.value
+          ? new Date(t.value + "T00:00:00").getTime() + 864e5
+          : Date.now();
+        if (!isFinite(from) || from <= 0) return toast(t("expRange"));
+        downloadStatsCsv(from, to);
+      }
       function downloadKeysCsv() {
         location.href =
           "/api/stats?export=keys-csv" +
@@ -2113,6 +2059,7 @@
             </button>
             <input id="ct-file" type="file" accept="image/*" multiple hidden onchange="addChatImgs(this.files)">
             <textarea id="ct-msg" rows="1" placeholder="${escAttr(t("cMsg"))}"></textarea>
+            <button class="sendbtn ghost" id="ct-clear" title="${escAttr(t("cClear"))}" onclick="clearChat()">${esc(t("cClear"))}</button>
             <button class="sendbtn" id="ct-send" onclick="sendChat()">${t("send")}</button>
           </div>
         </div>
@@ -2302,7 +2249,6 @@
           firstChunk = Date.now();
         try {
           const resp = await fetch("/api/chat", {
-            method: "POST",
             headers: { "Content-Type": "application/json" },
             body: JSON.stringify({
               model,
@@ -2551,7 +2497,6 @@
         btn.disabled = true;
         try {
           await api("/api/sources", {
-            method: "POST",
             body: JSON.stringify(payload),
           });
           toast(t("toastSaved"));
@@ -2567,7 +2512,6 @@
       async function delSource(name) {
         if (!confirm(tFmt("confirmDelSrc", name))) return;
         await api("/api/sources/" + encodeURIComponent(name), {
-          method: "DELETE",
         });
         toast(t("toastDelOk"));
         renderSources();
@@ -2722,9 +2666,6 @@
       <span class="scr-grip"><i></i><i></i><i></i></span>
     </div>`;
       }
-      function findSlots(li, ji) {
-        return sortState.lanes[li].models[ji];
-      }
       function paintSort(affected) {
         const cv = $("#scr-canvas");
         if (!cv) return;
@@ -3154,7 +3095,6 @@
           }),
         );
         await api("/api/auto", {
-          method: "PUT",
           body: JSON.stringify({ rules }),
         });
       }
@@ -3413,7 +3353,6 @@
         if (!name || !code) return toast(t("toastNeedAll"));
         try {
           await api("/api/adapters", {
-            method: "POST",
             body: JSON.stringify({ name, code }),
           });
           toast(t("toastUploaded"));
@@ -3427,7 +3366,6 @@
       async function delAdapter(name) {
         if (!confirm(tFmt("confirmDelAdp", name))) return;
         await api("/api/adapters/" + encodeURIComponent(name), {
-          method: "DELETE",
         });
         toast(t("toastDelOk"));
         renderAdapters();
@@ -3590,10 +3528,6 @@
         const p = String(comb).split("|");
         return { model: p[0], source: normSrc(p[1]) };
       }
-      function scopeUncomb(comb) {
-        const p = String(comb).split("|");
-        return { model: p[0], source: p[1] || "" };
-      }
       function fmtQuota(q) {
         q = +q || 0;
         if (!q) return "∞";
@@ -3631,7 +3565,6 @@
       }
       async function putScope(key, scopes) {
         await api("/api/keys/" + encodeURIComponent(key), {
-          method: "PUT",
           body: JSON.stringify({ models: scopes }),
         });
       }
@@ -3953,7 +3886,6 @@
         let j;
         try {
           j = await api("/api/keys", {
-            method: "POST",
             body: JSON.stringify({
               name,
               role: $("#kc-role").value,
@@ -3983,7 +3915,6 @@
         if (!confirm(tFmt("kDelConfirm", name || key))) return;
         try {
           await api("/api/keys/" + encodeURIComponent(key), {
-            method: "DELETE",
           });
           toast(t("toastDelOk"));
           loadKeys();