fix(ui): per-key 弹窗复用共享弹窗ID、编辑即落盘、空画布显示226个模型

截图看渲染 + 交互实测后发现的四个问题，都出在我自己新写的代码里。

一、弹窗用了全站共享的 #modal-wrap。
这个 id 是 App 内所有弹窗共用的，且允许多个同时存在（"添加档位"选择器就
开在本弹窗之上）。既有代码靠 .closest() 或 closeTopModal() 从按钮往上找，
是有效的——但本弹窗还要从画布侧被查（sortCanvasEl / keyAutoClose /
keyAutoInherit），那里没有按钮可走。实测点"添加档位"后 DOM 里同时有
modal-wrap=1 和 key-auto-modal=1，getElementById 会命中文档里的第一个，
也就是用户没在看的那一个：取消关掉错误的框，画布也可能解析到选择器上。
改为独立 id #key-auto-modal。

二、编辑即落盘，保存/取消形同虚设。
scrAddFromForm / sortScopeSave / scrDelSlot 等 6 处编辑后立刻调
persistAuto()。全局页这样是有意的（改动立即生效），但它和自己页面上那句
"点击保存排序后生效"的提示自相矛盾；在 per-key 弹窗里更严重——加一个槽位
就已经写进那个用户的链了，取消也无法撤销。收敛到 afterChainEdit()：
有 scope 时只提示、不落盘，保存是唯一写入口。

三、无独立链时画布显示全部 226 个模型。
注释写的是"显示空画布"，实现却是 buildLanes(idx, [], 'chat')——空 rules
会走 discovery 兜底，把每个源的模型全填进去。用户打开弹窗看到 226 个色块，
会以为这些就是这个密钥的链。改为空 rules 直接给 []。

四、"使用全局链"提示不随画布变化。
加完槽位后仍显示"该密钥使用全局 AUTO 链"，与旁边的色块直接矛盾。改为由
afterChainEdit 触发、按画布是否有内容决定去留。

另：批量替换时正则的缩进假设错了一次，把 afterChainEdit 自己改成了自调用
（无限递归），node --check 抓到后修掉。这类批量替换必须先过语法检查。

判据两条 + 变异：弹窗回到共享 id → 判红；去掉 scope 分支 → 判红。
CDP 实测：弹窗 id 唯一、添加后画布 0→1 块、添加后服务端 inherits=true
（未落盘）、取消后仍 inherits=true、选择器与弹窗并存互不干扰。

Co-Authored-By: ModelRouter <noreply@modelrouter.dev>

internal/gateway/ui_key_auto_test.go

@@ -204,3 +204,65 @@ func readFuncBody(t *testing.T, src, name string) string {
 	t.Fatalf("function %s body is unterminated", name)
 	return ""
 }
+
+// The per-key dialog must not share the app-wide #modal-wrap id.
+//
+// Every dialog in this file uses that id, and more than one can be open at
+// once (the "add slot" picker opens ON TOP of this one). Handlers resolve
+// their own dialog via `.closest()` from their button, which works — but this
+// dialog is also looked up from the CANVAS side (sortCanvasEl, keyAutoClose,
+// keyAutoInherit), where there is no button to walk up from.
+// getElementById("#modal-wrap") then returns whichever dialog comes first in
+// the document, i.e. not the one being edited: Cancel closed the wrong box and
+// the canvas could resolve to the picker's.
+func TestUIKeyAutoModalHasOwnID(t *testing.T) {
+	src := uiSource(t)
+	body := readFuncBody(t, src, "openKeyAutoModal")
+	if !strings.Contains(body, `wrap.id = "key-auto-modal"`) {
+		t.Fatal("openKeyAutoModal must give its dialog its own id, not the shared " +
+			"#modal-wrap (another dialog may be open on top of it)")
+	}
+	close := readFuncBody(t, src, "keyAutoClose")
+	if strings.Contains(close, `"modal-wrap"`) {
+		t.Fatal("keyAutoClose resolves the shared #modal-wrap; it would close " +
+			"whichever dialog comes first in the document")
+	}
+	if !strings.Contains(close, `"key-auto-modal"`) {
+		t.Fatal("keyAutoClose must resolve the per-key dialog by its own id")
+	}
+}
+
+// Editing a chain inside the per-key dialog must NOT persist it. That dialog
+// has Save and Cancel, so auto-writing on add/drag/delete meant the change was
+// already committed before Save and Cancel could not undo it.
+//
+// The global page is the opposite: it has always applied edits immediately.
+func TestUIKeyAutoEditsDoNotAutoPersist(t *testing.T) {
+	src := uiSource(t)
+	body := readFuncBody(t, src, "afterChainEdit")
+	if !strings.Contains(body, "if (sortState.scope)") {
+		t.Fatal("afterChainEdit must branch on sortState.scope")
+	}
+	// The scoped branch must return before reaching persistAuto.
+	iScope := strings.Index(body, "if (sortState.scope)")
+	iReturn := strings.Index(body[iScope:], "return")
+	iPersist := strings.Index(body, "persistAuto()")
+	if iScope < 0 || iReturn < 0 || iPersist < 0 {
+		t.Fatal("afterChainEdit no longer has the expected shape")
+	}
+	if iScope+iReturn > iPersist {
+		t.Fatal("the scoped branch reaches persistAuto() — a per-key edit would " +
+			"be written before Save")
+	}
+	// And it must not call itself (a regex-driven rewrite did exactly that).
+	if strings.Contains(body, "afterChainEdit()") {
+		t.Fatal("afterChainEdit calls itself: infinite recursion")
+	}
+	// Every in-canvas edit goes through it, so none of them bypass the check.
+	for _, fn := range []string{"scrAddFromForm", "sortScopeSave", "scrDelSlot"} {
+		b := readFuncBody(t, src, fn)
+		if strings.Contains(b, "persistAuto()") {
+			t.Fatalf("%s calls persistAuto() directly, bypassing afterChainEdit", fn)
+		}
+	}
+}