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/oss_uploader.py

@@ -37,7 +37,7 @@ class OSSUploader:
         url = self.bucket.sign_url("GET", object_name, 3600)
         return url, object_name
 
-    def delete_object(self, object_name: str):
+    def delete_object(self, object_name: str) -> None:
         """删除 OSS 对象"""
         self.bucket.delete_object(object_name)