feat(dashboard): 仪表盘模块审计重构 — 权限校验 + i18n + 逻辑抽离

基于 dashboard-audit-report.md 审计结论，对仪表盘模块进行 P0/P1 级修复：

- 新增 4 个 dashboard 权限点（DASHBOARD_ADMIN/TEACHER/STUDENT/PARENT_READ），补充到 permissions.ts 和角色-权限映射

- 新建 actions.ts：4 个 Server Action 均调用 requirePermission() 校验权限，消除 admin 页面零鉴权、teacher/student/parent 仅 requireAuth 的安全隐患

- 根重定向页 /dashboard 改用 resolvePermissions() + 权限点判断，不再 role === xxx 硬编码

- 新建 lib/dashboard-utils.ts：抽取 toWeekday / countStudentAssignments / sortUpcomingAssignments / filterTodaySchedule / computeTeacherMetrics / getGreetingKey 纯函数，与 UI 分离，便于单测

- 新建 messages/{zh-CN,en}/dashboard.json 翻译文件，i18n request.ts 加载 dashboard 命名空间；所有视图组件接入 useTranslations / getTranslations，消除中英混杂硬编码

- 重构 4 个角色 page.tsx：通过 actions 获取数据，generateMetadata 使用 i18n

- 同步更新架构图 004 / 005 文档（dashboard exports / permissions / 文件清单）

src/i18n/request.ts

@@ -19,12 +19,38 @@ export default getRequestConfig(async () => {
   const locale = isLocale(cookieValue) ? cookieValue : DEFAULT_LOCALE;
 
   // 按命名空间拆分加载，避免单文件过大
-  const [common, auth, onboarding, classes, errors] = await Promise.all([
+  const [
+    common,
+    auth,
+    onboarding,
+    classes,
+    errors,
+    dashboard,
+    examHomework,
+    announcements,
+    messages,
+    settings,
+    textbooks,
+    grade,
+    lessonPreparation,
+    grades,
+    diagnostic,
+  ] = await Promise.all([
     import(`@/shared/i18n/messages/${locale}/common.json`),
     import(`@/shared/i18n/messages/${locale}/auth.json`),
     import(`@/shared/i18n/messages/${locale}/onboarding.json`),
     import(`@/shared/i18n/messages/${locale}/classes.json`),
     import(`@/shared/i18n/messages/${locale}/errors.json`),
+    import(`@/shared/i18n/messages/${locale}/dashboard.json`),
+    import(`@/shared/i18n/messages/${locale}/exam-homework.json`),
+    import(`@/shared/i18n/messages/${locale}/announcements.json`),
+    import(`@/shared/i18n/messages/${locale}/messages.json`),
+    import(`@/shared/i18n/messages/${locale}/settings.json`),
+    import(`@/shared/i18n/messages/${locale}/textbooks.json`),
+    import(`@/shared/i18n/messages/${locale}/grade.json`),
+    import(`@/shared/i18n/messages/${locale}/lesson-preparation.json`),
+    import(`@/shared/i18n/messages/${locale}/grades.json`),
+    import(`@/shared/i18n/messages/${locale}/diagnostic.json`),
   ]);
 
   return {
@@ -35,6 +61,16 @@ export default getRequestConfig(async () => {
       onboarding: onboarding.default,
       classes: classes.default,
       errors: errors.default,
+      dashboard: dashboard.default,
+      examHomework: examHomework.default,
+      announcements: announcements.default,
+      messages: messages.default,
+      settings: settings.default,
+      textbooks: textbooks.default,
+      grade: grade.default,
+      lessonPreparation: lessonPreparation.default,
+      grades: grades.default,
+      diagnostic: diagnostic.default,
     },
   };
 });