fix: auto-fix code issues (cron)

- 修复缺失的导入 (re, csv, urllib.request)
- 修复未使用的导入清理
- 修复代码格式问题

backend/llm_client.py

@@ -119,8 +119,6 @@ class LLMClient:
         messages = [ChatMessage(role="user", content=prompt)]
         content = await self.chat(messages, temperature=0.1)
 
-        import re
-
         json_match = re.search(r"\{{.*?\}}", content, re.DOTALL)
         if not json_match:
             return [], []

backend/main.py

@@ -1110,8 +1110,6 @@ def extract_entities_with_llm(text: str) -> tuple[list[dict], list[dict]]:
         result = response.json()
         content = result["choices"][0]["message"]["content"]
 
-        import re
-
         json_match = re.search(r"\{{.*?\}}", content, re.DOTALL)
         if json_match:
             data = json.loads(json_match.group())