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/modules/lesson-preparation/actions-ai.ts

@@ -4,10 +4,11 @@ import { getTranslations } from "next-intl/server";
 import { requirePermission, PermissionDeniedError } from "@/shared/lib/auth-guard";
 import { Permissions } from "@/shared/types/permissions";
 import { suggestKnowledgePoints } from "./ai-suggest";
-import type { ActionState, LessonPlanDocument } from "./types";
+import { suggestKnowledgePointsSchema } from "./schema";
+import type { ActionState } from "@/shared/types/action-state";
 
 export async function suggestKnowledgePointsAction(input: {
-  doc: LessonPlanDocument;
+  doc: unknown;
   textbookId?: string;
   chapterId?: string;
 }): Promise<
@@ -17,12 +18,24 @@ export async function suggestKnowledgePointsAction(input: {
 > {
   const t = await getTranslations("lessonPreparation");
   try {
-    await requirePermission(Permissions.LESSON_PLAN_READ);
-    await requirePermission(Permissions.AI_CHAT);
+    const parsed = suggestKnowledgePointsSchema.safeParse(input);
+    if (!parsed.success) {
+      return { success: false, errors: parsed.error.flatten().fieldErrors };
+    }
+
+    // 并行校验两个权限点
+    await Promise.all([
+      requirePermission(Permissions.LESSON_PLAN_READ),
+      requirePermission(Permissions.AI_CHAT),
+    ]);
+
+    // 从 unknown 安全提取 nodes 数组：Zod 已校验 doc 是对象
+    const doc = parsed.data.doc;
+    const nodes = Array.isArray(doc.nodes) ? doc.nodes : [];
     const suggestions = await suggestKnowledgePoints(
-      input.doc,
-      input.textbookId,
-      input.chapterId,
+      { nodes },
+      parsed.data.textbookId,
+      parsed.data.chapterId,
     );
     return { success: true, data: { suggestions } };
   } catch (e) {