feat(web): 课堂求助 store 与全局 collab 连接

连接全局常驻，不跟题目页起落 —— 老师在任何页面都要能收到求助。
列表按题目聚合，同题多人时能一眼看出该全班讲。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1d8B3f4SXJwDvUY625eQd

apps/web/src/App.vue

@@ -6,10 +6,12 @@ import { useConfigStore } from "shared/store/config"
 import { useConfigUpdate } from "shared/composables/configUpdate"
 import { useMaxKB } from "shared/composables/maxkb"
 import { useUserStore } from "shared/store/user"
+import { useCollabStore } from "shared/store/collab"
 
 const isDark = useDark()
 const configStore = useConfigStore()
 const userStore = useUserStore()
+const collabStore = useCollabStore()
 
 // 初始化配置和实时更新
 onMounted(() => {
@@ -23,6 +25,17 @@ onMounted(() => {
 useConfigUpdate()
 useMaxKB()
 
+// 课堂求助通道。和 /ws/config 一样是全局常驻的：老师可能正在后台改题时
+// 收到求助，学生也要在排队期间一直挂着，所以不放在题目页里起落
+watch(
+  () => userStore.isAuthed,
+  (isAuthed) => {
+    if (isAuthed) collabStore.connect()
+    else collabStore.disconnect()
+  },
+  { immediate: true },
+)
+
 // 延迟加载 highlight.js，避免阻塞首屏
 const hljsInstance = ref<any>(null)
 const loadHighlightJS = async () => {