fix(settings): use deep copy to fix SQLAlchemy change detection

SQLAlchemy wasn't detecting changes when we modified the dict in place
and re-assigned the same object reference. Using deep copy ensures
the ORM sees the update.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/services/settings_service.py

@@ -49,12 +49,17 @@ async def update_user_profile(
 
 async def update_llm_config(user_id: str, config: dict, db: AsyncSession) -> dict:
     """更新 LLM 配置"""
+    import copy
+    logger.info(f"update_llm_config called with config keys: {list(config.keys())}")
+    logger.info(f"chat config: {config.get('chat')}")
     result = await db.execute(select(User).where(User.id == user_id))
     user = result.scalar_one_or_none()
     if not user:
         raise ValueError("用户不存在")
 
-    current = user.llm_config or {}
+    # 创建深拷贝，避免 SQLAlchemy 变更检测问题
+    current = copy.deepcopy(user.llm_config) or {}
+    logger.info(f"current llm_config before update: {current}")
     # 合并配置 - 直接替换整个类型配置列表
     for key, value in config.items():
         if value is not None:
@@ -69,8 +74,11 @@ async def update_llm_config(user_id: str, config: dict, db: AsyncSession) -> dic
                     current[key] = value
             else:
                 current[key] = value
+    logger.info(f"current llm_config after update: {current}")
     user.llm_config = current
     await db.commit()
+    await db.refresh(user)
+    logger.info(f"user.llm_config after refresh: {user.llm_config}")
     return current