refactor(server): steward 决策链路改用 LangGraph 编排

- 新增 StewardGraphPlannerService，用 LangGraph 状态图编排意图识别→流程判断→模型/规则分支→兜底，替代原 planner 内线性调用
- 新增 StewardGraphRuntimeService 编排运行时决策与槽位决策；StewardActionContracts/Executor 统一动作合约与执行
- steward_intent_agent/application_fact_resolver/runtime_chat 适配图执行器，config 暴露图相关开关
- pyproject/uv.lock 新增 langgraph 依赖
- 新增 graph_planner/graph_runtime/action_executor 测试，更新 intent_agent/planner/fact_resolver/runtime_chat/reimbursement 测试

server/tests/test_application_fact_resolver.py

@@ -22,6 +22,17 @@ def test_application_fact_resolver_extracts_travel_application_fields() -> None:
     assert facts["transport_mode"] == "train"
 
 
+def test_application_fact_resolver_drops_transport_prompt_from_application_reason() -> None:
+    facts = resolve_application_facts(
+        "2026-02-20 至 2026-02-23，去上海出差，辅助国网仿生产服务器部署，交通火车，直接提交",
+        "expense_application",
+        date(2026, 6, 24),
+    )
+
+    assert facts["reason"] == "辅助国网仿生产服务器部署"
+    assert facts["transport_mode"] == "train"
+
+
 def test_application_fact_resolver_preserves_reimbursement_transport_semantics() -> None:
     facts = resolve_application_facts(
         "报销昨天去北京客户现场沟通产生的出租车费用",