chore(todo): 添加中文 TODO 注释

- billing 中间件补充文案国际化 TODO

- 输入框补充 is_chatting 持久化 TODO

backend/packages/harness/deerflow/agents/middlewares/billing_middleware.py

@@ -174,6 +174,7 @@ def _extract_run_id(request: ModelRequest) -> str | None:  # noqa: ARG001
 
 def _reserve_failure_message(status_code: int | None) -> str:
     if status_code in _blocking_reserve_code_set():
+        # TODO: 将账单错误文案迁移到国际化资源中，按语言返回提示。
         return "The account balance is insufficient for this model call."
     return "Billing reservation failed. Please try again later."