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/llm_client.py

@@ -15,13 +15,11 @@ import httpx
 KIMI_API_KEY = os.getenv("KIMI_API_KEY", "")
 KIMI_BASE_URL = os.getenv("KIMI_BASE_URL", "https://api.kimi.com/coding")
 
-
 @dataclass
 class ChatMessage:
     role: str
     content: str
 
-
 @dataclass
 class EntityExtractionResult:
     name: str
@@ -29,7 +27,6 @@ class EntityExtractionResult:
     definition: str
     confidence: float
 
-
 @dataclass
 class RelationExtractionResult:
     source: str
@@ -37,7 +34,6 @@ class RelationExtractionResult:
     type: str
     confidence: float
 
-
 class LLMClient:
     """Kimi API 客户端"""
 
@@ -236,11 +232,9 @@ class LLMClient:
         messages = [ChatMessage(role="user", content=prompt)]
         return await self.chat(messages, temperature=0.3)
 
-
 # Singleton instance
 _llm_client = None
 
-
 def get_llm_client() -> LLMClient:
     global _llm_client
     if _llm_client is None: