fix(llm): add debug logging for custom API base URL configuration

- Add debug print statement to log custom API base URL when configured
- Improves troubleshooting and visibility into LiteLLM adapter initialization
- Helps developers verify correct API endpoint configuration during runtime

backend/app/services/llm/adapters/litellm_adapter.py

@@ -128,6 +128,7 @@ class LiteLLMAdapter(BaseLLMAdapter):
         # 设置 API Base URL
         if self._api_base:
             kwargs["api_base"] = self._api_base
+            print(f"🔗 使用自定义 API Base: {self._api_base}")
 
         # 设置超时
         kwargs["timeout"] = self.config.timeout