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_expansion_service.py

@@ -9,6 +9,7 @@ from app.models.project import Project
 from app.models.character import Character
 from app.models.chapter import Chapter
 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
 
@@ -531,7 +532,7 @@ class PlotExpansionService:
             cleaned_text = self.ai_service._clean_json_response(ai_response)
             
             # 解析JSON
-            chapter_plans = json.loads(cleaned_text)
+            chapter_plans = loads_json(cleaned_text)
             
             # 确保是列表
             if not isinstance(chapter_plans, list):
@@ -687,4 +688,4 @@ class PlotExpansionService:
 # 工厂函数
 def create_plot_expansion_service(ai_service: AIService) -> PlotExpansionService:
     """创建剧情展开服务实例"""
-    return PlotExpansionService(ai_service)
+    return PlotExpansionService(ai_service)