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

@@ -9,7 +9,6 @@ from datetime import datetime
 
 import oss2
 
-
 class OSSUploader:
     def __init__(self):
         self.access_key = os.getenv("ALI_ACCESS_KEY")
@@ -41,11 +40,9 @@ class OSSUploader:
         """删除 OSS 对象"""
         self.bucket.delete_object(object_name)
 
-
 # 单例
 _oss_uploader = None
 
-
 def get_oss_uploader() -> OSSUploader:
     global _oss_uploader
     if _oss_uploader is None: