feat(ai): 新增 AI 模块并集成至备课/错题集/试卷/改题四大业务场景

- 新增 src/modules/ai 独立模块，遵循三层架构（actions → services → shared/lib/ai）
- 通过 AiClientProvider + useAiClient 实现 React Context 依赖注入，业务组件零直接 import
- 6 个 Server Actions 均调用 requirePermission() 权限校验，返回 ActionState<T>
- withAiTracking 统一埋点，覆盖 chat/similar_question/grading_assist/lesson_content/question_variant/weakness_analysis
- 集成场景：作业批改 AiGradingAssist、错题集 AiErrorBookAnalysis、备课 AiLessonContentGenerator、试卷 AiQuestionVariantGenerator
- 全量 i18n（en/zh-CN ai.json），Error Boundary + Skeleton 边界处理
- 同步架构图 004/005，新增审计报告 ai-module-audit-report.md

src/i18n/request.ts

@@ -39,6 +39,7 @@ export default getRequestConfig(async () => {
     attendance,
     elective,
     school,
+    ai,
   ] = await Promise.all([
     import(`@/shared/i18n/messages/${locale}/common.json`),
     import(`@/shared/i18n/messages/${locale}/auth.json`),
@@ -59,6 +60,7 @@ export default getRequestConfig(async () => {
     import(`@/shared/i18n/messages/${locale}/attendance.json`),
     import(`@/shared/i18n/messages/${locale}/elective.json`),
     import(`@/shared/i18n/messages/${locale}/school.json`),
+    import(`@/shared/i18n/messages/${locale}/ai.json`),
   ]);
 
   return {
@@ -83,6 +85,7 @@ export default getRequestConfig(async () => {
       attendance: attendance.default,
       elective: elective.default,
       school: school.default,
+      ai: ai.default,
     },
   };
 });