feat(collab): 教师端弹框补上代码提示，语言跟着学生走

教师端的协作编辑器只有高亮和括号匹配，没装 autocompletion —— 老师替学生
写代码时没有下拉补全，只能盲敲。而且语言写死 cpp()，学生写 Python 时老师
看到的是 C 的高亮。

- 求助协议带上语言：help_request 记到 HelpRequest，accept 时写进 Room，
  room_open 发给两端；认不出的语言一律当 C（老客户端不带这个字段，而它
  以前就是写死 C 的）
- 新增 help_language / room_language：学生在排队或协作期间切语言，只更新
  语言，不动队列位置和房间；已开房就把新语言推给老师，弹框的高亮和补全
  实时跟着换
- CollabModal 装上 autocompletion，和学生端用同一套 enhanceCompletion +
  completeAnyWord；语言→高亮扩展的映射抽到 shared/extensions/language.ts
  两端共用，免得再分叉
- 学生端求助按钮合并状态提示：原来按钮旁边还挂一个 n-tag，一行工具栏在
  1280 的机房屏上放不下，改成状态全进 label（已求助 · 待接入 / 已求助 ·
  前面 N 人 / xxx 老师帮你中）

扩展数组变了 vue-codemirror 会整体 reconfigure，但 CM6 对已存在的
compartment 取 `compartments.get() || ext.inner`，collabDoc 那个装 yCollab
的 compartment 内容会被沿用，切语言、切主题都不会把协作弄断 —— 实跑验证过
双向同步、补全下拉、协作中切语言三条路径。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015APGLsyaCUa7XFMYAaCho4

apps/web/src/shared/components/CollabModal.vue

@@ -1,12 +1,18 @@
 <script setup lang="ts">
-import { cpp } from "@codemirror/lang-cpp"
 import { bracketMatching } from "@codemirror/language"
-import { closeBrackets } from "@codemirror/autocomplete"
+import {
+  autocompletion,
+  closeBrackets,
+  completeAnyWord,
+} from "@codemirror/autocomplete"
 import type { EditorView } from "@codemirror/view"
 import { Codemirror } from "vue-codemirror"
+import type { LANGUAGE } from "utils/types"
 import { oneDark } from "../themes/oneDark"
 import { smoothy } from "../themes/smoothy"
 import { styleTheme } from "shared/extensions/baseTheme"
+import { enhanceCompletion } from "shared/extensions/autocompletion"
+import { languageExtension } from "shared/extensions/language"
 import { useCollabDoc } from "../composables/collabDoc"
 import { useCollabStore } from "shared/store/collab"
 
@@ -26,12 +32,25 @@ const show = computed({
   },
 })
 
+/**
+ * 语言跟着学生走：room_open 带过来，学生协作期间切语言会再来一条 room_language。
+ * 取不到时按 C —— 和这里原来写死 cpp() 的表现一致。
+ */
+const language = computed<LANGUAGE>(() => collabStore.room?.language ?? "C")
+
 const extensions = computed(() => [
   styleTheme,
-  cpp(),
+  languageExtension(language.value),
   bracketMatching(),
   closeBrackets(),
   isDark.value ? oneDark : smoothy,
+  // 学生端有的补全这里必须也有：老师是在替学生写代码，缺了下拉菜单只能盲敲。
+  // 数组一变 vue-codemirror 会整体 reconfigure，但 collabDoc 那个 compartment
+  // 的内容会被 CM6 沿用（@codemirror/state 的 flatten 里 `compartments.get() ||
+  // ext.inner`），所以切语言、切主题都不会把 yCollab 弄掉
+  autocompletion({
+    override: [enhanceCompletion(language.value), completeAnyWord],
+  }),
   getInitialExtension(),
 ])
 
@@ -80,7 +99,7 @@ onUnmounted(() => {
     v-model:show="show"
     preset="card"
     :style="{ width: '80vw', maxWidth: '1100px' }"
-    :title="`正在帮 ${collabStore.room?.peerName ?? ''} · ${collabStore.room?.problemId ?? ''}`"
+    :title="`正在帮 ${collabStore.room?.peerName ?? ''} · ${collabStore.room?.problemId ?? ''} · ${language}`"
   >
     <template #header-extra>
       <n-button

apps/web/src/shared/components/SyncCodeEditor.vue

@@ -1,7 +1,4 @@
 <script lang="ts" setup>
-import { cpp } from "@codemirror/lang-cpp"
-import { python } from "@codemirror/lang-python"
-import { sql, SQLite } from "@codemirror/lang-sql"
 import { bracketMatching } from "@codemirror/language"
 import { Codemirror } from "vue-codemirror"
 import {
@@ -9,13 +6,13 @@ import {
   closeBrackets,
   completeAnyWord,
 } from "@codemirror/autocomplete"
-import type { Extension } from "@codemirror/state"
 import type { EditorView } from "@codemirror/view"
 import type { LANGUAGE } from "utils/types"
 import { oneDark } from "../themes/oneDark"
 import { smoothy } from "../themes/smoothy"
 import { styleTheme } from "shared/extensions/baseTheme"
 import { enhanceCompletion } from "shared/extensions/autocompletion"
+import { languageExtension } from "shared/extensions/language"
 import { useCollabDoc } from "../composables/collabDoc"
 import { useCollabStore } from "shared/store/collab"
 
@@ -40,11 +37,7 @@ const {
 } = defineProps<Props>()
 const code = defineModel<string>("value")
 
-const langExtension = computed((): Extension => {
-  if (language === "SQL")
-    return sql({ dialect: SQLite, upperCaseKeywords: true })
-  return ["Python2", "Python3"].includes(language) ? python() : cpp()
-})
+const langExtension = computed(() => languageExtension(language))
 
 const extensions = computed(() => [
   styleTheme,
@@ -96,6 +89,15 @@ watch(
   },
 )
 
+// 求助期间切了语言：同步给老师，他那边的高亮和补全跟着换。
+// 教师端不发 —— 这个组件在教师自己的题目页上也挂着，他的语言和房间无关
+watch(
+  () => language,
+  (lang) => {
+    if (!collabStore.isTeacher) collabStore.updateLanguage(lang)
+  },
+)
+
 onUnmounted(() => {
   stop()
   // 这个组件卸载意味着编辑器没了（切走页面、或者把语言切成流程图），