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/multimodal_entity_linker.py

@@ -80,7 +80,7 @@ class MultimodalEntityLinker:
     # 模态类型
     MODALITIES = ["audio", "video", "image", "document"]
 
-    def __init__(self, similarity_threshold: float = 0.85):
+    def __init__(self, similarity_threshold: float = 0.85) -> None:
         """
         初始化多模态实体关联器