fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/security_manager.py

@@ -196,7 +196,6 @@ class SecurityManager:
     }
 
     def __init__(self, db_path: str = "insightflow.db"):
-        self.db_path = db_path
         self.db_path = db_path
         # 预编译正则缓存
         self._compiled_patterns: dict[str, re.Pattern] = {}