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/zh-CN/dashboard.json

@@ -0,0 +1,124 @@
+{
+  "title": {
+    "admin": "管理控制台",
+    "teacher": "教师工作台",
+    "student": "学生中心",
+    "parent": "家长中心",
+    "root": "仪表盘"
+  },
+  "description": {
+    "admin": "用户、学习内容与活动全貌",
+    "teacher": "今日教学概览",
+    "student": "今日学习概览",
+    "parent": "查看孩子的学习概况"
+  },
+  "greeting": {
+    "morning": "早上好",
+    "afternoon": "下午好",
+    "evening": "晚上好",
+    "welcome": "欢迎回来",
+    "todayIs": "今天是 {date}，以下是今日概览。",
+    "overview": "以下是今日概览。"
+  },
+  "stats": {
+    "users": "用户总数",
+    "classes": "班级数",
+    "activeSessions": "活跃会话",
+    "homeworkPublished": "已发布作业",
+    "toGrade": "待批改",
+    "enrolledClasses": "已选课程",
+    "activeEnrollments": "有效选课",
+    "averageScore": "平均分",
+    "overallPerformance": "综合表现",
+    "noGradesYet": "暂无成绩",
+    "classRank": "班级排名",
+    "currentPosition": "当前名次",
+    "noRankingYet": "暂无排名",
+    "graded": "已批改",
+    "completedAssignments": "已完成作业",
+    "dueSoon": "即将到期",
+    "next7Days": "未来 7 天",
+    "overdue": "已逾期",
+    "needsAttention": "需要关注",
+    "needsGrading": "待批改",
+    "submissionsPendingReview": "待审核提交",
+    "activeAssignments": "进行中作业",
+    "publishedAndOngoing": "已发布且进行中",
+    "submissionRate": "提交率",
+    "overallCompletionRate": "总体完成率",
+    "acrossRecentAssignments": "近期作业平均"
+  },
+  "quickActions": {
+    "importUsers": "批量导入用户",
+    "importUsersDesc": "通过 Excel 批量创建用户账号",
+    "newAnnouncement": "发布公告",
+    "newAnnouncementDesc": "向全校或指定年级/班级发布通知",
+    "approveSchedule": "审批课表变更",
+    "approveScheduleDesc": "审核教师提交的课表变更与代课申请",
+    "autoSchedule": "自动排课",
+    "autoScheduleDesc": "基于规则自动生成周课表",
+    "fileManagement": "文件管理",
+    "fileManagementDesc": "查看与管理系统中所有上传文件",
+    "attendanceOverview": "考勤总览",
+    "attendanceOverviewDesc": "查看全校所有班级的考勤记录",
+    "grades": "成绩",
+    "attendance": "考勤",
+    "announcements": "通知",
+    "leaveRequest": "请假申请"
+  },
+  "todo": {
+    "title": "今日待办",
+    "toGrade": "待批改作业",
+    "todayAttendance": "今日待考勤",
+    "activeAssignments": "进行中作业",
+    "empty": "今日无待办事项"
+  },
+  "sections": {
+    "userGrowthTrend": "用户增长趋势（近30天）",
+    "homeworkSubmissionTrend": "作业提交趋势（近7天）",
+    "userRoles": "用户角色分布",
+    "content": "内容统计",
+    "homeworkActivity": "作业活动",
+    "recentUsers": "最近注册用户",
+    "viewAllUsers": "查看全部用户",
+    "pendingGrading": "待批改",
+    "todaySchedule": "今日课表",
+    "upcomingAssignments": "即将到期的作业",
+    "grades": "成绩",
+    "myClasses": "我的班级",
+    "gradeTrends": "成绩趋势"
+  },
+  "table": {
+    "name": "姓名",
+    "email": "邮箱",
+    "role": "角色",
+    "created": "创建时间"
+  },
+  "empty": {
+    "noUsers": "暂无用户",
+    "noUsersDesc": "数据库中暂无用户记录",
+    "noUsersYet": "暂无用户",
+    "seedHint": "初始化数据库以查看用户数据",
+    "allGraded": "全部批改完成！",
+    "allGradedDesc": "暂无待批改的提交。",
+    "noChildren": "未绑定孩子",
+    "noChildrenDesc": "您的账号尚未关联任何学生账号，请联系学校管理员完成绑定。",
+    "noStudent": "未找到学生用户",
+    "noStudentDesc": "请创建学生账号以查看仪表盘。",
+    "contactSupport": "联系客服"
+  },
+  "badge": {
+    "activeSessions": "{count} 个活跃会话",
+    "users": "{count} 位用户",
+    "childrenLinked": "已关联 {count} 个孩子"
+  },
+  "error": {
+    "loadFailed": "页面加载失败",
+    "loadFailedDesc": "抱歉，页面加载时发生了意外错误。请稍后重试。",
+    "retry": "重试"
+  },
+  "chart": {
+    "newUsers": "新增用户",
+    "newSubmissions": "新增提交"
+  }
+}