refactor(server): steward 意图改用声明式注册表编排

- 新增 steward_intent_registry，IntentDescriptor 统一描述意图的识别关键词、动作步骤构建、字段白名单与副作用集合，替代分散的 if/else
- 新增 steward_intent_bootstrap 注册 expense_application 等意图；新增 steward_query_executors 提供差旅标准查询的无副作用执行与城市/席别标签化输出
- action_contracts/action_executor/graph_planner/intent_agent/model_plan_builder/planner_extraction/fallback 适配注册表，识别与执行分发自动从注册表取数
- 新增 intent_registry/query_executors 测试，更新 intent_agent 测试

server/src/app/services/steward_action_contracts.py

@@ -26,8 +26,21 @@ class StewardActionPlanBuilder:
         return plan.model_copy(update={"tasks": tasks, "action_steps": plan_steps})
 
     def build_task_action_steps(self, task: StewardTask) -> list[StewardActionStep]:
+        from app.services.steward_intent_registry import get_intent
+
+        intent = get_intent(task.task_type)
+        if intent is not None:
+            return intent.action_steps_builder(task)
         if task.task_type == "expense_application":
-            return self._build_application_steps(task)
+            return self.build_application_steps(task)
+        if task.task_type == "reimbursement":
+            return self.build_reimbursement_steps(task)
+        return []
+
+    def build_application_steps(self, task: StewardTask) -> list[StewardActionStep]:
+        return self._build_application_steps(task)
+
+    def build_reimbursement_steps(self, task: StewardTask) -> list[StewardActionStep]:
         return self._build_reimbursement_steps(task)
 
     def _build_application_steps(self, task: StewardTask) -> list[StewardActionStep]: