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/components/ai-error-boundary.tsx

@@ -0,0 +1,88 @@
+"use client"
+
+import { Component, type ReactNode } from "react"
+import { AlertCircle, RefreshCw } from "lucide-react"
+import { useTranslations } from "next-intl"
+
+import { Button } from "@/shared/components/ui/button"
+import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+
+type AiErrorBoundaryProps = {
+  children: ReactNode
+  /** 自定义 fallback 渲染 */
+  fallback?: (error: Error, reset: () => void) => ReactNode
+  /** 错误回调（用于埋点） */
+  onError?: (error: Error, info: unknown) => void
+}
+
+type AiErrorBoundaryState = {
+  error: Error | null
+}
+
+/**
+ * AI 专用 Error Boundary
+ *
+ * 包裹所有 AI 数据区块，防止单个 AI 调用失败导致整页崩溃。
+ * 提供重试按钮与友好的错误提示。
+ */
+export class AiErrorBoundary extends Component<
+  AiErrorBoundaryProps,
+  AiErrorBoundaryState
+> {
+  constructor(props: AiErrorBoundaryProps) {
+    super(props)
+    this.state = { error: null }
+  }
+
+  static getDerivedStateFromError(error: Error): AiErrorBoundaryState {
+    return { error }
+  }
+
+  componentDidCatch(error: Error, info: unknown): void {
+    if (this.props.onError) {
+      this.props.onError(error, info)
+    }
+  }
+
+  private handleReset = (): void => {
+    this.setState({ error: null })
+  }
+
+  render(): ReactNode {
+    if (this.state.error) {
+      if (this.props.fallback) {
+        return this.props.fallback(this.state.error, this.handleReset)
+      }
+      return <DefaultAiErrorFallback error={this.state.error} onReset={this.handleReset} />
+    }
+    return this.props.children
+  }
+}
+
+function DefaultAiErrorFallback({
+  error,
+  onReset,
+}: {
+  error: Error
+  onReset: () => void
+}): ReactNode {
+  const t = useTranslations("ai")
+  return (
+    <Card className="border-destructive/30">
+      <CardHeader>
+        <CardTitle className="flex items-center gap-2 text-destructive">
+          <AlertCircle className="h-4 w-4" />
+          {t("error.boundaryTitle")}
+        </CardTitle>
+      </CardHeader>
+      <CardContent className="space-y-3">
+        <p className="text-sm text-muted-foreground">{t("error.boundaryDescription")}</p>
+        <p className="text-xs text-muted-foreground/70 font-mono">{error.message}</p>
+        <Button type="button" variant="outline" size="sm" onClick={onReset}>
+          <RefreshCw className="mr-1 h-3.5 w-3.5" />
+          {t("error.retry")}
+        </Button>
+      </CardContent>
+    </Card>
+  )
+}