refactor(dashboard): V2 审计重构 — i18n 补齐 + 共享抽象 + 单测 + a11y

V2 审计报告（docs/architecture/audit/dashboard-audit-report-v2.md）发现并修复：

- P0 i18n：10 个子组件硬编码字符串全部接入 next-intl（teacher-quick-actions /
  teacher-classes-card / teacher-homework-card / teacher-schedule /
  recent-submissions / teacher-grade-trends / student-grades-card /
  student-today-schedule-card / student-upcoming-assignments-card /
  admin-dashboard），新增 ~50 个翻译键
- P1 共享抽象：新增 DashboardGreetingHeader 组件，消除 teacher/student
  头部 90% 重复代码，两个 Header 改为薄包装
- P2 单测：为 6 个纯函数添加 31 个单元测试
  （tests/integration/dashboard/dashboard-utils.test.ts）
- P2 a11y：admin 表格 caption、teacher/student 视图语义化标签
  （header / section aria-label / aside aria-label）
- 同步架构图 004/005

src/modules/dashboard/components/student-dashboard/student-today-schedule-card.tsx

@@ -3,6 +3,7 @@
 import { useMemo } from "react"
 import Link from "next/link"
 import { CalendarDays, CalendarX } from "lucide-react"
+import { useTranslations } from "next-intl"
 
 import { Button } from "@/shared/components/ui/button"
 import { Badge } from "@/shared/components/ui/badge"
@@ -12,18 +13,15 @@ import { EmptyState } from "@/shared/components/ui/empty-state"
 import { cn } from "@/shared/lib/utils"
 import type { StudentTodayScheduleItem } from "@/modules/dashboard/types"
 
-/**
- * Parse "HH:MM" time string into minutes since midnight for comparison.
- */
 const timeToMinutes = (t: string): number => {
   const [h, m] = t.split(":").map(Number)
   return (h ?? 0) * 60 + (m ?? 0)
 }
 
 export function StudentTodayScheduleCard({ items }: { items: StudentTodayScheduleItem[] }) {
+  const t = useTranslations("dashboard")
   const hasSchedule = items.length > 0
 
-  // Compute current/next class status based on client time
   const { currentId, nextId } = useMemo(() => {
     const now = new Date()
     const nowMin = now.getHours() * 60 + now.getMinutes()
@@ -49,18 +47,18 @@ export function StudentTodayScheduleCard({ items }: { items: StudentTodaySchedul
       <CardHeader className="flex flex-row items-center justify-between">
         <CardTitle className="flex items-center gap-2">
           <CalendarDays className="h-4 w-4 text-muted-foreground" />
-          Today&apos;s Schedule
+          {t("sections.todaySchedule")}
         </CardTitle>
         <Button asChild variant="outline" size="sm">
-          <Link href="/student/schedule">View all</Link>
+          <Link href="/student/schedule">{t("quickActions.viewAll")}</Link>
         </Button>
       </CardHeader>
       <CardContent>
         {!hasSchedule ? (
           <EmptyState
             icon={CalendarX}
-            title="No classes today"
-            description="Your timetable is clear for today."
+            title={t("empty.noClassesToday")}
+            description={t("empty.noClassesTodayDesc")}
             className="border-none h-72"
           />
         ) : (
@@ -74,14 +72,14 @@ export function StudentTodayScheduleCard({ items }: { items: StudentTodaySchedul
               if (isCurrent) {
                 return (
                   <Badge className="shrink-0 bg-emerald-500 text-white hover:bg-emerald-500">
-                    In Progress
+                    {t("badge.inProgress")}
                   </Badge>
                 )
               }
               if (isNext) {
                 return (
                   <Badge variant="outline" className="shrink-0 border-primary text-primary">
-                    Up Next
+                    {t("badge.upNext")}
                   </Badge>
                 )
               }