fix: MCP插件TimeoutError修复 + 多项Bug修复和性能优化

- fix: MCP插件管理接口改为后台任务，修复TimeoutError
- fix: MCP连接失败后上下文清理的cancel scope错误
- feat: MCP插件后台注册添加重试机制
- fix: 限制每章自动创建伏笔数量上限
- fix: 修复JSON非法转义字符清洗
- fix: SSE流式生成添加心跳保活
- fix: 职业生成改用POST请求避免URL长度限制
- perf: 使用torch CPU版本加速Docker构建
- fix: 自动修复JSON字符串值中的裸换行符
- feat: 集成json5容错解析器

backend/app/services/plot_analyzer.py

@@ -2,6 +2,7 @@
 from typing import Dict, Any, List, Optional, Callable, Awaitable
 from sqlalchemy.ext.asyncio import AsyncSession
 from app.services.ai_service import AIService
+from app.services.json_helper import loads_json
 from app.services.prompt_service import prompt_service, PromptService
 from app.logger import get_logger
 import json
@@ -277,7 +278,7 @@ class PlotAnalyzer:
             cleaned = self.ai_service._clean_json_response(response)
             
             # 尝试解析JSON
-            result = json.loads(cleaned)
+            result = loads_json(cleaned)
             
             # 验证必要字段
             required_fields = ['hooks', 'plot_points', 'scores']
@@ -594,4 +595,4 @@ def get_plot_analyzer(ai_service: AIService) -> PlotAnalyzer:
     global _plot_analyzer_instance
     if _plot_analyzer_instance is None:
         _plot_analyzer_instance = PlotAnalyzer(ai_service)
-    return _plot_analyzer_instance
+    return _plot_analyzer_instance