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/app/(dashboard)/teacher/dashboard/error.tsx

@@ -1,18 +1,20 @@
 "use client"
 
 import { AlertCircle } from "lucide-react"
+import { useTranslations } from "next-intl"
 
 import { EmptyState } from "@/shared/components/ui/empty-state"
 
 export default function TeacherDashboardError({ reset }: { error: Error & { digest?: string }; reset: () => void }) {
+  const t = useTranslations("dashboard")
   return (
     <div className="flex h-full flex-col items-center justify-center space-y-4 p-8">
       <EmptyState
         icon={AlertCircle}
-        title="页面加载失败"
-        description="抱歉，页面加载时发生了意外错误。请稍后重试。"
+        title={t("error.loadFailed")}
+        description={t("error.loadFailedDesc")}
         action={{
-          label: "重试",
+          label: t("error.retry"),
           onClick: () => reset(),
         }}
         className="border-none shadow-none h-auto"

src/app/(dashboard)/teacher/dashboard/page.tsx

@@ -1,37 +1,21 @@
+import type { Metadata } from "next"
 import type { JSX } from "react"
+import { getTranslations } from "next-intl/server"
+
 import { TeacherDashboardView } from "@/modules/dashboard/components/teacher-dashboard/teacher-dashboard-view"
-import { getClassSchedule, getTeacherClasses, getTeacherIdForMutations } from "@/modules/classes/data-access"
-import { getHomeworkAssignments, getHomeworkSubmissions, getTeacherGradeTrends } from "@/modules/homework/data-access"
-import { getUserBasicInfo } from "@/modules/users/data-access"
-import { getAuthContext } from "@/shared/lib/auth-guard"
+import { getTeacherDashboardAction } from "@/modules/dashboard/actions"
 
 export const dynamic = "force-dynamic"
 
-export const metadata = { title: "Dashboard - Next_Edu" }
+export async function generateMetadata(): Promise<Metadata> {
+  const t = await getTranslations("dashboard")
+  return {
+    title: t("title.teacher"),
+    description: t("description.teacher"),
+  }
+}
 
 export default async function TeacherDashboardPage(): Promise<JSX.Element> {
-  await getAuthContext()
-  const teacherId = await getTeacherIdForMutations()
-
-  const [classes, schedule, assignments, submissions, teacherProfile, gradeTrends] = await Promise.all([
-    getTeacherClasses({ teacherId }),
-    getClassSchedule({ teacherId }),
-    getHomeworkAssignments({ creatorId: teacherId }),
-    getHomeworkSubmissions({ creatorId: teacherId }),
-    getUserBasicInfo(teacherId),
-    getTeacherGradeTrends(teacherId),
-  ])
-
-  return (
-    <TeacherDashboardView
-      data={{
-        classes,
-        schedule,
-        assignments,
-        submissions,
-        teacherName: teacherProfile?.name ?? "Teacher",
-        gradeTrends,
-      }}
-    />
-  )
+  const data = await getTeacherDashboardAction()
+  return <TeacherDashboardView data={data} />
 }