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/main.py

@@ -2381,8 +2381,6 @@ async def create_attribute_template_endpoint(
     if not DB_AVAILABLE:
         raise HTTPException(status_code=500, detail="Database not available")
 
-    from db_manager import AttributeTemplate
-
     db = get_db_manager()
     project = db.get_project(project_id)
     if not project:
@@ -2602,8 +2600,6 @@ async def batch_set_entity_attributes_endpoint(
     if not DB_AVAILABLE:
         raise HTTPException(status_code=500, detail="Database not available")
 
-    from db_manager import EntityAttribute
-
     db = get_db_manager()
     entity = db.get_entity(entity_id)
     if not entity:
@@ -8667,8 +8663,6 @@ async def get_branding_css(tenant_id: str):
     manager = get_tenant_manager()
     css = manager.get_branding_css(tenant_id)
 
-    from fastapi.responses import PlainTextResponse
-
     return PlainTextResponse(content=css, media_type="text/css")