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)/student/dashboard/page.tsx

@@ -1,101 +1,42 @@
+import type { Metadata } from "next"
+import type { JSX } from "react"
+import { getTranslations } from "next-intl/server"
+
 import { StudentDashboard } from "@/modules/dashboard/components/student-dashboard/student-dashboard-view"
-import { getStudentClasses, getStudentSchedule } from "@/modules/classes/data-access"
-import { getStudentDashboardGrades, getStudentHomeworkAssignments } from "@/modules/homework/data-access"
-import { getCurrentStudentUser } from "@/modules/users/data-access"
+import { getStudentDashboardAction } from "@/modules/dashboard/actions"
 import { EmptyState } from "@/shared/components/ui/empty-state"
 import { UserX } from "lucide-react"
-import type { StudentHomeworkProgressStatus } from "@/modules/homework/types"
 
 export const dynamic = "force-dynamic"
 
-export const metadata = { title: "Dashboard - Next_Edu" }
-
-const toWeekday = (d: Date): 1 | 2 | 3 | 4 | 5 | 6 | 7 => {
-  // getDay() 返回 0(周日)-6(周六)，转换为 1-7（周一为 1）
-  const WEEKDAY_MAP = [7, 1, 2, 3, 4, 5, 6] as const
-  const day = d.getDay()
-  if (day < 0 || day > 6) {
-    throw new Error(`Invalid day from getDay(): ${day}`)
+export async function generateMetadata(): Promise<Metadata> {
+  const t = await getTranslations("dashboard")
+  return {
+    title: t("title.student"),
+    description: t("description.student"),
   }
-  return WEEKDAY_MAP[day]
 }
 
-export default async function StudentDashboardPage() {
-  const student = await getCurrentStudentUser()
-  if (!student) {
+export default async function StudentDashboardPage(): Promise<JSX.Element> {
+  const t = await getTranslations("dashboard")
+  const { student, dashboardProps } = await getStudentDashboardAction()
+
+  if (!student || !dashboardProps) {
     return (
       <EmptyState
-        title="No user found"
-        description="Create a student user to see dashboard."
+        title={t("empty.noStudent")}
+        description={t("empty.noStudentDesc")}
         icon={UserX}
         className="border-none shadow-none h-auto"
       />
     )
   }
 
-  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 in7Days = new Date(now)
-  in7Days.setDate(in7Days.getDate() + 7)
-
-  // 单次遍历统计，避免重复 filter（PERF-04）
-  let dueSoonCount = 0
-  let overdueCount = 0
-  let gradedCount = 0
-  for (const a of assignments) {
-    const status: StudentHomeworkProgressStatus = a.progressStatus
-    if (status === "graded") {
-      gradedCount++
-      continue
-    }
-    if (!a.dueAt) continue
-    const due = new Date(a.dueAt)
-    if (due >= now && due <= in7Days) {
-      dueSoonCount++
-    } else if (due < now) {
-      overdueCount++
-    }
-  }
-
-  const todayWeekday = toWeekday(now)
-  const todayScheduleItems = schedule
-    .filter((s) => s.weekday === todayWeekday)
-    .map((s) => ({
-      id: s.id,
-      classId: s.classId,
-      className: s.className,
-      course: s.course,
-      startTime: s.startTime,
-      endTime: s.endTime,
-      location: s.location ?? null,
-    }))
-    .sort((a, b) => a.startTime.localeCompare(b.startTime))
-
-  const upcomingAssignments = [...assignments]
-    .sort((a, b) => {
-      const aDue = a.dueAt ? new Date(a.dueAt).getTime() : Number.POSITIVE_INFINITY
-      const bDue = b.dueAt ? new Date(b.dueAt).getTime() : Number.POSITIVE_INFINITY
-      return aDue - bDue
-    })
-    .slice(0, 6)
-
   return (
     <div className="space-y-8">
       <StudentDashboard
         studentName={student.name}
-        enrolledClassCount={classes.length}
-        dueSoonCount={dueSoonCount}
-        overdueCount={overdueCount}
-        gradedCount={gradedCount}
-        todayScheduleItems={todayScheduleItems}
-        upcomingAssignments={upcomingAssignments}
-        grades={grades}
+        {...dashboardProps}
       />
     </div>
   )