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/modules/dashboard/actions.ts

@@ -0,0 +1,146 @@
+"use server"
+
+import { cache } from "react"
+
+import { requirePermission } from "@/shared/lib/auth-guard"
+import { Permissions } from "@/shared/types/permissions"
+import { getClassSchedule, getStudentClasses, getStudentSchedule, getTeacherClasses, getTeacherIdForMutations } from "@/modules/classes/data-access"
+import {
+  getHomeworkAssignments,
+  getHomeworkSubmissions,
+  getStudentDashboardGrades,
+  getStudentHomeworkAssignments,
+  getTeacherGradeTrends,
+} from "@/modules/homework/data-access"
+import { getCurrentStudentUser, getUserBasicInfo } from "@/modules/users/data-access"
+import { getParentDashboardData } from "@/modules/parent/data-access"
+
+import { getAdminDashboardData } from "./data-access"
+import type {
+  AdminDashboardData,
+  StudentDashboardProps,
+  TeacherDashboardData,
+} from "./types"
+import type { ParentDashboardData } from "@/modules/parent/types"
+import {
+  computeTeacherMetrics,
+  countStudentAssignments,
+  sortUpcomingAssignments,
+  toWeekday,
+  filterTodaySchedule,
+  type TeacherDashboardMetrics,
+} from "./lib/dashboard-utils"
+
+/**
+ * 获取管理员仪表盘数据。
+ * 权限：DASHBOARD_ADMIN_READ
+ */
+export async function getAdminDashboardAction(): Promise<AdminDashboardData> {
+  const ctx = await requirePermission(Permissions.DASHBOARD_ADMIN_READ)
+  return getAdminDashboardData(ctx.dataScope)
+}
+
+/**
+ * 获取教师仪表盘数据（含派生指标）。
+ * 权限：DASHBOARD_TEACHER_READ
+ */
+export async function getTeacherDashboardAction(): Promise<TeacherDashboardData & {
+  metrics: TeacherDashboardMetrics
+}> {
+  await requirePermission(Permissions.DASHBOARD_TEACHER_READ)
+  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),
+  ])
+
+  const metrics = computeTeacherMetrics(
+    classes,
+    schedule,
+    assignments,
+    submissions,
+    gradeTrends,
+    new Date(),
+  )
+
+  return {
+    classes,
+    schedule,
+    assignments,
+    submissions,
+    teacherName: teacherProfile?.name ?? "Teacher",
+    gradeTrends,
+    metrics,
+  }
+}
+
+/**
+ * 获取学生仪表盘数据（含派生指标）。
+ * 权限：DASHBOARD_STUDENT_READ
+ */
+export async function getStudentDashboardAction(): Promise<{
+  student: { id: string; name: string } | null
+  dashboardProps: Omit<StudentDashboardProps, "studentName"> | null
+}> {
+  await requirePermission(Permissions.DASHBOARD_STUDENT_READ)
+  const student = await getCurrentStudentUser()
+  if (!student) {
+    return { student: null, dashboardProps: null }
+  }
+
+  const [classes, schedule, assignments, grades] = await Promise.all([
+    getStudentClasses(student.id),
+    getStudentSchedule(student.id),
+    getStudentHomeworkAssignments(student.id),
+    getStudentDashboardGrades(student.id),
+  ])
+
+  const now = new Date()
+  const stats = countStudentAssignments(assignments, now)
+  const todayWeekday = toWeekday(now)
+  const todayScheduleItems = filterTodaySchedule(schedule, todayWeekday)
+  const upcomingAssignments = sortUpcomingAssignments(assignments, 6)
+
+  return {
+    student: { id: student.id, name: student.name },
+    dashboardProps: {
+      enrolledClassCount: classes.length,
+      dueSoonCount: stats.dueSoonCount,
+      overdueCount: stats.overdueCount,
+      gradedCount: stats.gradedCount,
+      todayScheduleItems,
+      upcomingAssignments,
+      grades,
+    },
+  }
+}
+
+/**
+ * 获取家长仪表盘数据。
+ * 权限：DASHBOARD_PARENT_READ
+ */
+export async function getParentDashboardAction(): Promise<{
+  data: ParentDashboardData | null
+  hasChildren: boolean
+}> {
+  const ctx = await requirePermission(Permissions.DASHBOARD_PARENT_READ)
+
+  // 非 admin 且 dataScope 非 children 类型时，无孩子数据
+  if (
+    ctx.dataScope.type !== "all" &&
+    !(ctx.dataScope.type === "children" && ctx.dataScope.childrenIds.length > 0)
+  ) {
+    return { data: null, hasChildren: false }
+  }
+
+  const data = await getParentDashboardData(ctx.userId)
+  return { data, hasChildren: data.children.length > 0 }
+}
+
+/** 缓存版本（用于 RSC 直接调用，不走 Server Action 协议） */
+export const getCachedAdminDashboard = cache(getAdminDashboardAction)