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/hooks/use-lesson-plan-editor.ts

@@ -9,7 +9,6 @@ import type {
   LessonPlanEdge,
   LessonPlanNode,
 } from "../types";
-import { BLOCK_TYPE_LABELS } from "../constants";
 
 interface EditorState {
   planId: string;
@@ -24,7 +23,7 @@ interface EditorState {
   setPlanId: (planId: string) => void;
   hydrate: (planId: string, title: string, doc: LessonPlanDocument) => void;
 
-  addNode: (type: BlockType, position?: { x: number; y: number }) => string;
+  addNode: (type: BlockType, position?: { x: number; y: number }, title?: string) => string;
   updateNode: (id: string, patch: Partial<Block>) => void;
   updateNodePosition: (id: string, position: { x: number; y: number }) => void;
   removeNode: (id: string) => void;
@@ -76,13 +75,13 @@ export const useLessonPlanEditor = create<EditorState>((set, get) => ({
       selectedNodeId: null,
     }),
 
-  addNode: (type, position) => {
+  addNode: (type, position, title) => {
     const id = createId();
     const nodeCount = get().doc.nodes.length;
     const node: LessonPlanNode = {
       id,
       type,
-      title: BLOCK_TYPE_LABELS[type],
+      title: title ?? type, // 调用方应传入翻译后的标题，fallback 为 type 键
       data: defaultData(type),
       order: nodeCount,
       position: position ?? {