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/lesson-preparation/constants.ts

@@ -1,21 +1,26 @@
 import type { BlockType, TemplateBlockSkeleton, TemplateScope } from "./types";
 
-// block 类型 → 中文默认标题
-export const BLOCK_TYPE_LABELS: Record<BlockType, string> = {
-  objective: "教学目标",
-  key_point: "教学重难点",
-  import: "导入",
-  new_teaching: "新授",
-  consolidation: "巩固练习",
-  summary: "课堂小结",
-  homework: "作业布置",
-  blackboard: "板书设计",
-  text_study: "文本研习",
-  exercise: "练习/作业",
-  rich_text: "自定义环节",
-  reflection: "教学反思",
+// block 类型 → i18n 键（实际文本由 useTranslations("lessonPreparation").blockType.${type} 翻译）
+// 保留此映射用于：1) 新节点默认标题的 i18n 键查找 2) 类型守卫
+export const BLOCK_TYPE_KEYS: Record<BlockType, string> = {
+  objective: "objective",
+  key_point: "key_point",
+  import: "import",
+  new_teaching: "new_teaching",
+  consolidation: "consolidation",
+  summary: "summary",
+  homework: "homework",
+  blackboard: "blackboard",
+  text_study: "text_study",
+  exercise: "exercise",
+  rich_text: "rich_text",
+  reflection: "reflection",
 };
 
+// 向后兼容：保留 BLOCK_TYPE_LABELS 名称但值为 i18n 键（实际翻译由组件层完成）
+// @deprecated 使用 BLOCK_TYPE_KEYS 或 useTranslations("lessonPreparation").blockType.${type} 替代
+export const BLOCK_TYPE_LABELS: Record<BlockType, string> = BLOCK_TYPE_KEYS;
+
 // 富文本类 block（共享同一编辑组件）
 export const RICH_TEXT_BLOCK_TYPES: BlockType[] = [
   "objective",
@@ -100,8 +105,11 @@ export const SYSTEM_TEMPLATES: SystemTemplateDef[] = [
   },
 ];
 
-export const LESSON_PLAN_STATUS_LABELS: Record<string, string> = {
-  draft: "草稿",
-  published: "已发布",
-  archived: "已归档",
+export const LESSON_PLAN_STATUS_KEYS: Record<string, string> = {
+  draft: "draft",
+  published: "published",
+  archived: "archived",
 };
+
+// @deprecated 使用 useTranslations("lessonPreparation").status.${key} 替代
+export const LESSON_PLAN_STATUS_LABELS: Record<string, string> = LESSON_PLAN_STATUS_KEYS;