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/teacher-dashboard/teacher-homework-card.tsx

@@ -1,5 +1,6 @@
 import Link from "next/link"
 import { PenTool, Calendar, Plus } from "lucide-react"
+import { getTranslations } from "next-intl/server"
 
 import { Badge } from "@/shared/components/ui/badge"
 import { Button } from "@/shared/components/ui/button"
@@ -8,16 +9,18 @@ import { EmptyState } from "@/shared/components/ui/empty-state"
 import { cn, formatDate } from "@/shared/lib/utils"
 import type { HomeworkAssignmentListItem } from "@/modules/homework/types"
 
-export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssignmentListItem[] }) {
+export async function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssignmentListItem[] }) {
+  const t = await getTranslations("dashboard")
+
   return (
     <Card>
       <CardHeader className="flex flex-row items-center justify-between pb-3">
         <CardTitle className="text-base flex items-center gap-2">
           <PenTool className="h-4 w-4 text-muted-foreground" />
-          Homework
+          {t("sections.homework")}
         </CardTitle>
-        <Button asChild size="icon" variant="ghost" className="h-8 w-8">
-          <Link href="/teacher/homework/assignments/create" title="Create new assignment">
+        <Button asChild size="icon" variant="ghost" className="h-8 w-8" title={t("quickActions.createNewAssignment")}>
+          <Link href="/teacher/homework/assignments/create">
             <Plus className="h-4 w-4" />
           </Link>
         </Button>
@@ -26,9 +29,9 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
         {assignments.length === 0 ? (
           <EmptyState
             icon={PenTool}
-            title="No assignments"
-            description="Create an assignment to get started."
-            action={{ label: "Create", href: "/teacher/homework/assignments/create" }}
+            title={t("empty.noAssignments")}
+            description={t("empty.noAssignmentsDesc")}
+            action={{ label: t("quickActions.create"), href: "/teacher/homework/assignments/create" }}
             className="border-none h-48"
           />
         ) : (
@@ -36,7 +39,7 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
             {assignments.slice(0, 6).map((a) => {
               const isPublished = a.status === "published"
               const isDraft = a.status === "draft"
-              
+
               return (
                 <Link
                   key={a.id}
@@ -47,7 +50,7 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
                     <div className="flex items-center gap-2 mb-0.5">
                       <div className={cn(
                         "h-2 w-2 rounded-full",
-                        isPublished ? "bg-emerald-500" : 
+                        isPublished ? "bg-emerald-500" :
                         isDraft ? "bg-amber-400" : "bg-muted-foreground"
                       )} />
                       <div className="font-medium truncate text-sm group-hover:text-primary transition-colors">
@@ -58,7 +61,7 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
                       {a.sourceExamTitle}
                     </div>
                   </div>
-                  
+
                   <div className="flex flex-col items-end gap-1">
                     {a.dueAt ? (
                       <div className="flex items-center text-xs text-muted-foreground tabular-nums">
@@ -66,10 +69,10 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
                         {formatDate(a.dueAt)}
                       </div>
                     ) : (
-                      <span className="text-[10px] text-muted-foreground italic">No due date</span>
+                      <span className="text-[10px] text-muted-foreground italic">{t("schedule.noDueDate")}</span>
                     )}
-                    <Badge 
-                      variant="outline" 
+                    <Badge
+                      variant="outline"
                       className={cn(
                         "text-[10px] h-4 px-1.5 capitalize font-normal border-transparent bg-muted/50",
                         isPublished && "text-emerald-600 bg-emerald-500/10",
@@ -84,7 +87,7 @@ export function TeacherHomeworkCard({ assignments }: { assignments: HomeworkAssi
             })}
             <div className="pt-2">
               <Button asChild variant="link" size="sm" className="w-full text-muted-foreground h-auto py-1 text-xs">
-                <Link href="/teacher/homework/assignments">View all assignments</Link>
+                <Link href="/teacher/homework/assignments">{t("quickActions.viewAllAssignments")}</Link>
               </Button>
             </div>
           </div>