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/shared/i18n/messages/zh-CN/ai.json

@@ -0,0 +1,109 @@
+{
+  "chat": {
+    "title": "AI 助手",
+    "placeholder": "请输入您的问题...",
+    "inputLabel": "消息输入",
+    "send": "发送",
+    "thinking": "AI 正在思考...",
+    "maxReached": "已达到最大消息数",
+    "clear": "清空对话"
+  },
+  "provider": {
+    "label": "AI 服务商",
+    "placeholder": "选择服务商",
+    "loading": "加载服务商中...",
+    "default": "默认",
+    "description": "选择本次操作使用的 AI 配置。",
+    "manage": "管理",
+    "manageTitle": "AI 服务商设置",
+    "manageDescription": "新建服务商或更新已有配置。"
+  },
+  "suggestion": {
+    "title": "AI 建议",
+    "generate": "生成建议",
+    "regenerate": "重新生成",
+    "loading": "AI 思考中...",
+    "empty": "暂无建议",
+    "error": "生成建议失败",
+    "loaded": "建议已加载",
+    "selected": "已选择建议",
+    "select": "选择",
+    "difficulty": "难度"
+  },
+  "grading": {
+    "title": "AI 批改建议",
+    "suggestedScore": "建议分数",
+    "confidence": "置信度",
+    "feedback": "反馈",
+    "reasoning": "评分依据",
+    "applyScore": "应用分数",
+    "applyFeedback": "应用反馈",
+    "loading": "AI 批改中...",
+    "error": "AI 批改失败",
+    "notAvailable": "此题型不支持 AI 批改"
+  },
+  "errorBook": {
+    "similarQuestions": "相似题目",
+    "weaknessAnalysis": "薄弱点分析",
+    "studyPlan": "学习计划",
+    "recommendedResources": "推荐资源",
+    "weakAreas": "薄弱领域",
+    "severity": {
+      "high": "高",
+      "medium": "中",
+      "low": "低"
+    }
+  },
+  "lessonPrep": {
+    "generateContent": "生成内容",
+    "generateActivity": "建议活动",
+    "generateAssessment": "生成评估",
+    "generateQuestion": "生成讨论题",
+    "loading": "生成中...",
+    "error": "内容生成失败"
+  },
+  "exam": {
+    "generate": "生成",
+    "generating": "生成中...",
+    "preview": "预览",
+    "queue": "加入队列",
+    "queueRunning": "运行中",
+    "queueQueued": "排队中",
+    "backgroundTasks": "后台任务",
+    "taskStatus": {
+      "queued": "排队中",
+      "running": "生成中",
+      "success": "已完成",
+      "failed": "失败"
+    },
+    "openPreview": "打开预览",
+    "sourceText": "试卷原文",
+    "sourceTextPlaceholder": "粘贴试卷文本以解析为题目",
+    "sourceTextDesc": "AI 将从文本中提取题目和结构。",
+    "generationTitle": "AI 生成",
+    "generationDesc": "粘贴试卷文本并生成结构化预览。"
+  },
+  "error": {
+    "invalidInput": "输入数据无效",
+    "chatFailed": "AI 请求失败",
+    "suggestionFailed": "AI 建议失败",
+    "gradingFailed": "AI 批改失败",
+    "contentFailed": "内容生成失败",
+    "variantFailed": "题目变体生成失败",
+    "analysisFailed": "薄弱点分析失败",
+    "boundaryTitle": "AI 功能错误",
+    "boundaryDescription": "处理 AI 请求时发生错误，请重试。",
+    "retry": "重试",
+    "unauthorized": "您没有使用 AI 功能的权限",
+    "providerNotConfigured": "AI 服务商未配置，请联系管理员。"
+  },
+  "capability": {
+    "chat": "AI 对话",
+    "examGenerate": "AI 出题",
+    "gradingAssist": "AI 辅助批改",
+    "lessonContent": "AI 备课内容",
+    "questionVariant": "AI 题目变体",
+    "similarQuestion": "AI 相似题",
+    "weaknessAnalysis": "AI 薄弱点分析"
+  }
+}