feat(webui): 密钥配额表单 + 修复弹窗关闭错对象

功能：让 per-key 配额在 WebUI 里可配置可见，之前的实现只有 API 与
config.yaml 能配。

- 密钥卡片头部显示配额徽标（token / 请求数 + 重置窗口），admin key
  不显示编辑入口（服务端本就永不受限，给入口只会让人以为配了会生效）。
- 新增「配额」编辑弹窗：token 配额、请求数配额、重置周期（复用既有
  的 period 词表与 n-hour 联动），预填从 canvas 的 data-* 读。
- 创建密钥弹窗同步加配额字段；选 admin 角色时自动禁用（同样因为服务端
  忽略 admin 的配额）。
- 「我的密钥」页新增 KEY-WIDE QUOTA 列，用户能看到自己这把 key 的预算。

修一个真 bug：保存弹窗用 $("#modal-wrap") 关闭自己，而全站弹窗共用这个
id、且可以叠加（seed key 提示就盖在密钥页上）。实测（共享 Chromium
CDP，seed 提示与配额弹窗共存）确认：保存后被移除的是 seed 提示，配额表单
反而留在屏幕上 —— 症状是「保存了但弹窗没关」，指向的方向完全错。改为用
点击的按钮 btn.closest("#modal-wrap") 解析自己的弹窗。createKey 有同样
问题，一并修。既有文件里另有 7 处同样写法，未动（不在本次范围，且新判据
只对本次改的两处断言，避免误伤）。

判据新增 internal/gateway/ui_quota_contract_test.go（6 例）：
- 两个表单必须用 .closest 解析自己的弹窗
- putScope 必须带上 4 个配额字段（API 视其为指针，省略=清空预算）
- 创建请求必须真的发出配额字段
- **数据流判据**：徽标要真读 k.token_quota 等、编辑表单要真读
  canvas 写的 data-kquota 等。只查字面量存在会漏 —— 字段躺在死分支里
  判据照样通过（这是本轮实际踩到的：keyCapBadges 经 keyPeriodSuffix
  间接读 k.period，被判据抓到后我把读取显式化而不是放宽判据）
- 弹窗扫描先剥注释，否则修复说明里引用的字面量会被当成违规
- 复用既有 ui_contract_test.go 的 jsFunctionBody（大括号配平）；
  自己第一版用 2000 字符固定窗口，被长注释顶开后仍在窗口外命中后面
  函数的同名字段，读起来像通过 —— 窗口法在这里是假判据

7 个变异全部被抓（unsafe 关闭、putScope 丢字段、createKey 丢字段、
徽标不读字段、canvas 不写 data-*、kq-hours 改名、周期词表缺项）。

浏览器实测（共享 Chromium CDP，真实进程 + 加密配置）：
- 徽标渲染 1.0K·1h / 5×·1h；编辑框预填 1000/5/hour，hours 框按周期联动
- 保存后回读 250000/77/nhour/6，徽标更新为 250.0K·6h，toast Saved
- 零 JS 异常
- **关键回归**：编辑模型 scope 后配额仍是 250000/77/nhour，未被清空
- 创建带配额的 key，服务端确认 {t:50000,r:300,p:week,role:user}
- user 视角「我的密钥」显示 777·1h 与 9×·1h

文档：README.md / README_EN.md 补「密钥用量配额」小节（配置示例、
周期词表、429 语义、admin 豁免、整点分桶最晚晚 1 小时释放、PUT 的
省略 vs 0 语义、429 响应样例），特性列表各加一条。

README_EN.md

@@ -38,6 +38,10 @@ Extracted and independently evolved from the multi-source LLM adapter layer of
   `reasoning_content`, `tool_calls`, `usage`).
 - **Image generation**: `POST /v1/images/generations`, routed to models with
   `kind: image`.
+- **Per-key usage quota**: each key carries its own token and request caps plus a
+  reset period (hour/week/month/custom N hours), shared across every model that
+  key may use. Exhaustion answers 429 + `Retry-After` so a client resumes when
+  the window rolls over; admin keys are never capped.
 - **Multimodal**: `content` arrays (`image_url` etc.) pass through losslessly;
   Anthropic/Gemini/Ollama are translated automatically.
 - **LuaJIT VM**: golua-binding LuaJIT; each adapter has its own VM + worker
@@ -176,6 +180,54 @@ under the `keys` field of the runtime file (encrypted at rest):
   `Authorization: Bearer <key>`.
 - Deleting a key removes it from the store immediately.
 
+#### Per-key usage quota
+
+Each key can cap its own spend and reset period. Two levels apply at once:
+
+```yaml
+keys:
+  - key: sk-gw-<hex>
+    role: user
+    name: agent-alice
+    # ---- key-wide (across every model) ----
+    token_quota: 5000000    # total token budget for this window, 0 = unlimited
+    req_quota: 20000        # requests per window, 0 = unlimited
+    period: nhour           # "" | hour | week | month | nhour
+    hours: 6                # n-hour only: resets every 6 hours
+    # ---- per-model scope (optional) ----
+    models:
+      - model: m1
+        token_quota: 1000000
+        period: hour
+      - model: AUTO
+```
+
+- `period`: empty = never resets (lifetime total); `hour` / `week` / `month` =
+  fixed windows; `nhour` + `hours` = a custom hour count. **A misspelled
+  period is rejected at write time** rather than silently becoming a
+  never-resetting quota.
+- The key-wide cap is one budget shared by every model the key may use;
+  quotas under `models[]` are counted per model. Both are isolated per key —
+  one key's traffic never drains another's budget.
+- Usage counts chat, streaming and image requests, and survives a restart by
+  replaying the audit log (40 days retained, covering the longest `month`
+  window).
+- An exhausted quota returns **429 + `Retry-After`**
+  (`rate_limit_exceeded`) so a client resumes when the window rolls over; a
+  model the key may not use stays 403. **Admin keys are never capped**, so a
+  cap can never lock the operator out.
+- Buckets are whole unix hours, so a window frees up at most an hour late
+  (deliberately freeing late rather than overspending).
+- On `PUT /api/keys/{key}` the quota fields are optional: omitting them keeps
+  the stored caps, sending `0` explicitly lifts a cap. Editing only the model
+  scope never clears a budget that was already set.
+
+```
+HTTP/1.1 429 Too Many Requests
+Retry-After: 2100
+{"error":{"type":"rate_limit_exceeded","message":"key token quota exceeded (5000000/5000000, resets every 6h)"}}
+```
+
 ### Model routing
 
 `/v1/chat/completions` `model` resolution order: