feat: 报销预审会话状态管理与工作台交互增强

- 新增差旅报销会话状态管理与对话模型重构
- 增强风险观测服务与运行时聊天上下文作用域
- 优化工作台图标资源、助理意图识别与摘要工具
- 完善报销创建视图样式与差旅详情页标准调整交互
- 补充风险观测、运行时聊天与报销端点测试覆盖

server/src/app/services/steward_constants.py

@@ -0,0 +1,18 @@
+from __future__ import annotations
+
+
+BUSINESS_CANONICAL_FIELD_ORDER = (
+    "expense_type",
+    "time_range",
+    "location",
+    "reason",
+    "amount",
+    "transport_mode",
+    "attachments",
+    "customer_name",
+    "merchant_name",
+    "department_name",
+    "employee_name",
+    "employee_no",
+)
+BUSINESS_CANONICAL_FIELDS = frozenset(BUSINESS_CANONICAL_FIELD_ORDER)