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_planner_fallback.py

@@ -63,6 +63,11 @@ class StewardPlannerFallbackMixin:
             return None
         if any(keyword in compact for keyword in STEWARD_BUSINESS_SIGNAL_KEYWORDS):
             return None
+        # 补充注册表里各意图声明的信号词(如查询类"差旅标准"等),避免被判 off_topic
+        from app.services.steward_intent_registry import all_signal_keywords
+
+        if any(keyword in compact for keyword in all_signal_keywords()):
+            return None
 
         if StewardPlannerFallbackMixin._looks_like_greeting(compact):
             return STEWARD_OFF_TOPIC_SCENARIO_GREETING