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-grades-card.tsx

@@ -2,7 +2,9 @@
 
 import Link from "next/link"
 import { BarChart3 } from "lucide-react"
+import { useTranslations } from "next-intl"
 
+import { Button } from "@/shared/components/ui/button"
 import { ChartCardShell } from "@/shared/components/charts/chart-card-shell"
 import { TrendLineChart } from "@/shared/components/charts/trend-line-chart"
 import { Table, TableBody, TableCell, TableHead, TableHeader, TableRow } from "@/shared/components/ui/table"
@@ -10,6 +12,7 @@ import { formatDate } from "@/shared/lib/utils"
 import type { StudentDashboardGradeProps } from "@/modules/homework/types"
 
 export function StudentGradesCard({ grades }: { grades: StudentDashboardGradeProps }) {
+  const t = useTranslations("dashboard")
   const hasGradeTrend = grades.trend.length > 0
   const hasRecentGrades = grades.recent.length > 0
 
@@ -26,13 +29,20 @@ export function StudentGradesCard({ grades }: { grades: StudentDashboardGradePro
 
   return (
     <ChartCardShell
-      title="Recent Grades"
+      title={t("sections.recentGrades")}
       icon={BarChart3}
       iconClassName="text-muted-foreground"
       isEmpty={!hasGradeTrend}
-      emptyTitle="No graded work yet"
-      emptyDescription="Finish and submit assignments to see your score trend."
+      emptyTitle={t("empty.noGradedWork")}
+      emptyDescription={t("empty.noGradedWorkDesc")}
       emptyClassName="h-72"
+      action={
+        hasGradeTrend ? (
+          <Button asChild variant="outline" size="sm">
+            <Link href="/student/grades">{t("quickActions.viewAll")}</Link>
+          </Button>
+        ) : null
+      }
     >
       <div className="space-y-4">
         <div className="rounded-md border bg-card p-4">
@@ -41,7 +51,7 @@ export function StudentGradesCard({ grades }: { grades: StudentDashboardGradePro
             series={[
               {
                 dataKey: "score",
-                name: "Score (%)",
+                name: t("chart.scorePercent"),
                 color: "hsl(var(--primary))",
                 dotRadius: 4,
                 activeDotRadius: 6,
@@ -56,13 +66,13 @@ export function StudentGradesCard({ grades }: { grades: StudentDashboardGradePro
           {latestGrade ? (
             <div className="mt-3 flex items-center justify-between text-sm text-muted-foreground">
               <div>
-                Latest:{" "}
+                {t("chart.latest")}:{" "}
                 <span className="font-medium text-foreground tabular-nums">
                   {Math.round(latestGrade.percentage)}%
                 </span>
               </div>
               <div>
-                Points:{" "}
+                {t("chart.points")}:{" "}
                 <span className="font-medium text-foreground tabular-nums">
                   {latestGrade.score}/{latestGrade.maxScore}
                 </span>
@@ -76,9 +86,9 @@ export function StudentGradesCard({ grades }: { grades: StudentDashboardGradePro
             <Table>
               <TableHeader>
                 <TableRow className="bg-muted/50">
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Assignment</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">Score</TableHead>
-                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">When</TableHead>
+                  <TableHead className="text-xs font-medium uppercase text-muted-foreground">{t("table.assignment")}</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">{t("table.when")}</TableHead>
                 </TableRow>
               </TableHeader>
               <TableBody>