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/ai/schema.ts

@@ -0,0 +1,134 @@
+import { z } from "zod"
+
+// ---------------------------------------------------------------------------
+// 基础校验
+// ---------------------------------------------------------------------------
+
+export const AiChatMessageSchema = z.object({
+  role: z.enum(["system", "user", "assistant"]),
+  content: z.string().min(1).max(8000),
+})
+
+export const AiChatInputSchema = z.object({
+  messages: z.array(AiChatMessageSchema).min(1).max(50),
+  providerId: z.string().min(1).optional(),
+})
+
+// ---------------------------------------------------------------------------
+// 业务场景校验
+// ---------------------------------------------------------------------------
+
+export const SimilarQuestionInputSchema = z.object({
+  questionText: z.string().min(1).max(4000),
+  questionType: z.string().min(1),
+  subject: z.string().optional(),
+  knowledgePointIds: z.array(z.string()).optional(),
+  count: z.number().int().min(1).max(10).optional(),
+})
+
+export const GradingInputSchema = z.object({
+  questionText: z.string().min(1).max(4000),
+  questionType: z.string().min(1),
+  studentAnswer: z.string().min(1).max(8000),
+  correctAnswer: z.string().optional(),
+  maxScore: z.number().int().min(1).max(100),
+  subject: z.string().optional(),
+})
+
+export const LessonContentInputSchema = z.object({
+  topic: z.string().min(1).max(500),
+  subject: z.string().optional(),
+  grade: z.string().optional(),
+  textbookId: z.string().optional(),
+  chapterId: z.string().optional(),
+  contentType: z.enum(["activity", "assessment", "question", "material"]),
+  additionalContext: z.string().max(2000).optional(),
+})
+
+export const QuestionVariantInputSchema = z.object({
+  originalQuestion: z.object({
+    text: z.string().min(1).max(4000),
+    type: z.string().min(1),
+    difficulty: z.number().int().min(1).max(5).optional(),
+    options: z
+      .array(
+        z.object({
+          id: z.string().min(1),
+          text: z.string().min(1),
+          isCorrect: z.boolean().optional(),
+        })
+      )
+      .optional(),
+    answer: z.string().optional(),
+  }),
+  subject: z.string().optional(),
+  variantType: z.enum(["same_knowledge_point", "different_difficulty", "different_format"]),
+})
+
+export const WeaknessAnalysisInputSchema = z.object({
+  studentId: z.string().min(1),
+  subjectId: z.string().optional(),
+  errorItems: z
+    .array(
+      z.object({
+        questionText: z.string().min(1),
+        questionType: z.string().min(1),
+        knowledgePointIds: z.array(z.string()).optional(),
+        errorCount: z.number().int().min(1),
+        masteryLevel: z.number().int().min(0).max(5),
+      })
+    )
+    .min(1)
+    .max(100),
+})
+
+// ---------------------------------------------------------------------------
+// AI 返回结果校验（用于解析 AI JSON 输出）
+// ---------------------------------------------------------------------------
+
+export const SimilarQuestionResultSchema = z.object({
+  text: z.string().min(1),
+  type: z.string().min(1),
+  difficulty: z.number().int().min(1).max(5).optional(),
+  options: z.array(z.object({ id: z.string(), text: z.string() })).optional(),
+  answer: z.string().optional(),
+  explanation: z.string().optional(),
+})
+
+export const SimilarQuestionListSchema = z.array(SimilarQuestionResultSchema)
+
+export const GradingSuggestionSchema = z.object({
+  suggestedScore: z.number().min(0),
+  confidence: z.number().min(0).max(1),
+  feedback: z.string(),
+  reasoning: z.string(),
+})
+
+export const LessonContentResultSchema = z.object({
+  title: z.string().min(1),
+  content: z.string().min(1),
+  metadata: z.record(z.string(), z.unknown()).optional(),
+})
+
+export const QuestionVariantResultSchema = z.object({
+  text: z.string().min(1),
+  type: z.string().min(1),
+  difficulty: z.number().int().min(1).max(5),
+  options: z
+    .array(z.object({ id: z.string(), text: z.string(), isCorrect: z.boolean() }))
+    .optional(),
+  answer: z.string().optional(),
+  explanation: z.string().optional(),
+})
+
+export const WeaknessAnalysisResultSchema = z.object({
+  weakAreas: z.array(
+    z.object({
+      area: z.string().min(1),
+      severity: z.enum(["high", "medium", "low"]),
+      suggestion: z.string().min(1),
+    })
+  ),
+  studyPlan: z.string().min(1),
+  recommendedResources: z.array(z.string()),
+})