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-upcoming-assignments-card.tsx

@@ -1,5 +1,6 @@
 import Link from "next/link"
 import { PenTool } from "lucide-react"
+import { getTranslations } from "next-intl/server"
 
 import { Badge } from "@/shared/components/ui/badge"
 import { Button } from "@/shared/components/ui/button"
@@ -14,11 +15,11 @@ import {
   STUDENT_HOMEWORK_PROGRESS_LABEL,
 } from "@/modules/homework/types"
 
-const getActionLabel = (status: string) => {
-  if (status === "graded") return "Review"
-  if (status === "submitted") return "View"
-  if (status === "in_progress") return "Continue"
-  return "Start"
+const getActionLabelKey = (status: string): "action.review" | "action.view" | "action.continue" | "action.start" => {
+  if (status === "graded") return "action.review"
+  if (status === "submitted") return "action.view"
+  if (status === "in_progress") return "action.continue"
+  return "action.start"
 }
 
 const getActionVariant = (status: string): "default" | "secondary" | "outline" => {
@@ -33,12 +34,13 @@ const getDueUrgency = (dueAt: string | null) => {
   const diffHours = (due.getTime() - now.getTime()) / (1000 * 60 * 60)
 
   if (diffHours < 0) return "overdue"
-  if (diffHours < 48) return "urgent" // 2 days
-  if (diffHours < 120) return "warning" // 5 days
+  if (diffHours < 48) return "urgent"
+  if (diffHours < 120) return "warning"
   return "normal"
 }
 
-export function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomingAssignments: StudentHomeworkAssignmentListItem[] }) {
+export async function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomingAssignments: StudentHomeworkAssignmentListItem[] }) {
+  const t = await getTranslations("dashboard")
   const hasAssignments = upcomingAssignments.length > 0
 
   return (
@@ -46,18 +48,18 @@ export function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomi
       <CardHeader className="flex flex-row items-center justify-between">
         <CardTitle className="text-base flex items-center gap-2">
           <PenTool className="h-4 w-4 text-muted-foreground" />
-          Upcoming Assignments
+          {t("sections.upcomingAssignments")}
         </CardTitle>
         <Button asChild variant="outline" size="sm">
-          <Link href="/student/learning/assignments">View all</Link>
+          <Link href="/student/learning/assignments">{t("quickActions.viewAll")}</Link>
         </Button>
       </CardHeader>
       <CardContent>
         {!hasAssignments ? (
           <EmptyState
             icon={PenTool}
-            title="No assignments"
-            description="You have no assigned homework right now."
+            title={t("empty.noAssignmentsStudent")}
+            description={t("empty.noAssignmentsStudentDesc")}
             className="border-none h-72"
           />
         ) : (
@@ -65,18 +67,18 @@ export function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomi
             <Table>
               <TableHeader>
                 <TableRow className="bg-muted/50">
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Title</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Status</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Due</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Score</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground text-right">Action</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">{t("table.title")}</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">{t("table.status")}</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">{t("table.due")}</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">{t("table.score")}</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground text-right">{t("table.action")}</TableHead>
                 </TableRow>
               </TableHeader>
               <TableBody>
                 {upcomingAssignments.map((a) => {
                   const urgency = getDueUrgency(a.dueAt)
                   const isGraded = a.progressStatus === "graded"
-                  
+
                   return (
                     <TableRow key={a.id} className="h-12">
                       <TableCell className="font-medium">
@@ -85,7 +87,7 @@ export function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomi
                             {a.title}
                           </Link>
                           {!isGraded && urgency === "overdue" && (
-                             <Badge variant="destructive" className="h-5 px-1.5 text-[10px] uppercase">Late</Badge>
+                             <Badge variant="destructive" className="h-5 px-1.5 text-[10px] uppercase">{t("badge.late")}</Badge>
                           )}
                         </div>
                       </TableCell>
@@ -107,7 +109,7 @@ export function StudentUpcomingAssignmentsCard({ upcomingAssignments }: { upcomi
                       <TableCell className="text-right">
                         <Button asChild size="sm" variant={getActionVariant(a.progressStatus)} className="h-7 text-xs">
                           <Link href={`/student/learning/assignments/${a.id}`}>
-                            {getActionLabel(a.progressStatus)}
+                            {t(getActionLabelKey(a.progressStatus))}
                           </Link>
                         </Button>
                       </TableCell>