refactor(backend): update user agent service and tests

- services/user_agent.py: update user agent service
- tests/test_orchestrator_service.py: update orchestrator tests

server/tests/test_orchestrator_service.py

@@ -631,9 +631,9 @@ def test_orchestrator_treats_expense_narrative_as_draft_instead_of_ar_query() ->
     assert payload["trace_summary"]["intent"] == "draft"
     assert payload["trace_summary"]["tool_count"] == 0
     assert "应收场景数据" not in payload["result"]["message"]
-    assert payload["result"]["message"].startswith("我先根据你当前提供的信息完成了初步识别")
+    assert payload["result"]["message"].startswith("识别到您希望报销一笔“业务招待费”费用")
     review_payload = payload["result"]["review_payload"]
-    assert review_payload["intent_summary"].startswith("我理解你这次想报销业务招待费。")
+    assert review_payload["intent_summary"].startswith("识别到您希望报销一笔“业务招待费”费用。")
     assert review_payload["missing_slots"] == ["客户名称", "参与人员", "票据附件"]
     slot_map = {item["key"]: item for item in review_payload["slot_cards"]}
     assert slot_map["time_range"]["raw_value"] == "今天"