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/api_key_manager.py

@@ -51,7 +51,7 @@ class ApiKeyManager:
         self.db_path = db_path
         self._init_db()
 
-    def _init_db(self):
+    def _init_db(self) -> None:
         """初始化数据库表"""
         with sqlite3.connect(self.db_path) as conn:
             conn.executescript("""
@@ -331,7 +331,7 @@ class ApiKeyManager:
             conn.commit()
             return cursor.rowcount > 0
 
-    def update_last_used(self, key_id: str):
+    def update_last_used(self, key_id: str) -> None:
         """更新最后使用时间"""
         with sqlite3.connect(self.db_path) as conn:
             conn.execute(