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/shared/i18n/messages/zh-CN/lesson-preparation.json

@@ -56,7 +56,14 @@
     "titleLabel": "课案标题",
     "titlePlaceholder": "例如：《秋天》第一课时",
     "blockCount": "{count} 个环节",
-    "blankHint": "从空白开始"
+    "blankHint": "从空白开始",
+    "names": {
+      "tpl_regular": "常规课",
+      "tpl_review": "复习课",
+      "tpl_experiment": "实验课",
+      "tpl_inquiry": "探究课",
+      "tpl_blank": "空白模板"
+    }
   },
   "editor": {
     "canvasEmpty": "画布为空",
@@ -87,7 +94,9 @@
     "auto": "自动",
     "manual": "手动保存",
     "revert": "回退到此版本",
+    "revertTitle": "确认回退",
     "revertConfirm": "确认回退到 v{versionNo}？将生成新版本。",
+    "revertSuccess": "已回退到 v{versionNo}",
     "autoLabel": "自动版本"
   },
   "knowledgePoint": {
@@ -193,6 +202,7 @@
     "retry": "重试"
   },
   "confirm": {
-    "archive": "确认归档此课案？"
+    "archive": "确认归档此课案？",
+    "archiveTitle": "确认归档"
   }
 }