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/plugin_manager.py

@@ -163,7 +163,7 @@ class PluginManager:
         self._handlers = {}
         self._register_default_handlers()
 
-    def _register_default_handlers(self):
+    def _register_default_handlers(self) -> None:
         """注册默认处理器"""
         self._handlers[PluginType.CHROME_EXTENSION] = ChromeExtensionHandler(self)
         self._handlers[PluginType.FEISHU_BOT] = BotHandler(self, "feishu")
@@ -371,7 +371,7 @@ class PluginManager:
 
         return cursor.rowcount > 0
 
-    def record_plugin_usage(self, plugin_id: str):
+    def record_plugin_usage(self, plugin_id: str) -> None:
         """记录插件使用"""
         conn = self.db.get_conn()
         now = datetime.now().isoformat()
@@ -826,9 +826,6 @@ class BotHandler:
 
     async def _send_feishu_message(self, session: BotSession, message: str, msg_type: str) -> bool:
         """发送飞书消息"""
-        import base64
-        import hashlib
-
         timestamp = str(int(time.time()))
 
         # 生成签名
@@ -851,9 +848,6 @@ class BotHandler:
 
     async def _send_dingtalk_message(self, session: BotSession, message: str, msg_type: str) -> bool:
         """发送钉钉消息"""
-        import base64
-        import hashlib
-
         timestamp = str(round(time.time() * 1000))
 
         # 生成签名
@@ -1358,7 +1352,7 @@ class WebDAVSyncManager:
 _plugin_manager = None
 
 
-def get_plugin_manager(db_manager=None):
+def get_plugin_manager(db_manager=None) -> None:
     """获取 PluginManager 单例"""
     global _plugin_manager
     if _plugin_manager is None: