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/shared/i18n/messages/en/dashboard.json

@@ -0,0 +1,124 @@
+{
+  "title": {
+    "admin": "Admin Console",
+    "teacher": "Teacher Workspace",
+    "student": "Student Center",
+    "parent": "Parent Center",
+    "root": "Dashboard"
+  },
+  "description": {
+    "admin": "System overview across users, learning content, and activity.",
+    "teacher": "Today's teaching overview.",
+    "student": "Today's learning overview.",
+    "parent": "An overview of your children."
+  },
+  "greeting": {
+    "morning": "Good morning",
+    "afternoon": "Good afternoon",
+    "evening": "Good evening",
+    "welcome": "Welcome back",
+    "todayIs": "Today is {date}. Here's your overview.",
+    "overview": "Here's today's overview."
+  },
+  "stats": {
+    "users": "Users",
+    "classes": "Classes",
+    "activeSessions": "Active sessions",
+    "homeworkPublished": "Homework (published)",
+    "toGrade": "To grade",
+    "enrolledClasses": "Enrolled Classes",
+    "activeEnrollments": "Active enrollments",
+    "averageScore": "Average Score",
+    "overallPerformance": "Overall performance",
+    "noGradesYet": "No grades yet",
+    "classRank": "Class Rank",
+    "currentPosition": "Current position",
+    "noRankingYet": "No ranking yet",
+    "graded": "Graded",
+    "completedAssignments": "Completed assignments",
+    "dueSoon": "Due Soon",
+    "next7Days": "Next 7 days",
+    "overdue": "Overdue",
+    "needsAttention": "Needs attention",
+    "needsGrading": "Needs Grading",
+    "submissionsPendingReview": "Submissions pending review",
+    "activeAssignments": "Active Assignments",
+    "publishedAndOngoing": "Published and ongoing",
+    "submissionRate": "Submission Rate",
+    "overallCompletionRate": "Overall completion rate",
+    "acrossRecentAssignments": "Across recent assignments"
+  },
+  "quickActions": {
+    "importUsers": "Import Users",
+    "importUsersDesc": "Batch create user accounts via Excel",
+    "newAnnouncement": "New Announcement",
+    "newAnnouncementDesc": "Publish notices to the whole school or specific grades/classes",
+    "approveSchedule": "Approve Schedule Changes",
+    "approveScheduleDesc": "Review schedule changes and substitute teacher requests",
+    "autoSchedule": "Auto Scheduling",
+    "autoScheduleDesc": "Auto-generate weekly schedules based on rules",
+    "fileManagement": "File Management",
+    "fileManagementDesc": "View and manage all uploaded files",
+    "attendanceOverview": "Attendance Overview",
+    "attendanceOverviewDesc": "View attendance records for all classes",
+    "grades": "Grades",
+    "attendance": "Attendance",
+    "announcements": "Announcements",
+    "leaveRequest": "Leave Request"
+  },
+  "todo": {
+    "title": "Today's To-Do",
+    "toGrade": "Homework to grade",
+    "todayAttendance": "Attendance to take",
+    "activeAssignments": "Active assignments",
+    "empty": "No to-do items today"
+  },
+  "sections": {
+    "userGrowthTrend": "User Growth Trend (Last 30 Days)",
+    "homeworkSubmissionTrend": "Homework Submission Trend (Last 7 Days)",
+    "userRoles": "User Roles",
+    "content": "Content",
+    "homeworkActivity": "Homework Activity",
+    "recentUsers": "Recent Users",
+    "viewAllUsers": "View all users",
+    "pendingGrading": "Pending Grading",
+    "todaySchedule": "Today's Schedule",
+    "upcomingAssignments": "Upcoming Assignments",
+    "grades": "Grades",
+    "myClasses": "My Classes",
+    "gradeTrends": "Grade Trends"
+  },
+  "table": {
+    "name": "Name",
+    "email": "Email",
+    "role": "Role",
+    "created": "Created"
+  },
+  "empty": {
+    "noUsers": "No users",
+    "noUsersDesc": "No user records found.",
+    "noUsersYet": "No users yet",
+    "seedHint": "Seed the database to see users here.",
+    "allGraded": "All graded!",
+    "allGradedDesc": "No submissions pending review.",
+    "noChildren": "No children linked",
+    "noChildrenDesc": "Your account is not linked to any student accounts yet. Please contact the school administrator to link your child.",
+    "noStudent": "No student found",
+    "noStudentDesc": "Create a student user to see dashboard.",
+    "contactSupport": "Contact support"
+  },
+  "badge": {
+    "activeSessions": "{count} active sessions",
+    "users": "{count} users",
+    "childrenLinked": "{count} children linked"
+  },
+  "error": {
+    "loadFailed": "Page load failed",
+    "loadFailedDesc": "Sorry, an unexpected error occurred while loading the page. Please try again later.",
+    "retry": "Retry"
+  },
+  "chart": {
+    "newUsers": "New users",
+    "newSubmissions": "New submissions"
+  }
+}