feat: 新增预算后端服务与差旅风险规则库

后端新增预算模型、端点和服务模块，支持预算 CRUD 和余额
查询，清理旧生成规则文件并替换为按严重等级分类的差旅风
险规则库，优化认证权限和报销单访问策略，新增财务规则目
录和演示数据构建脚本，前端预算中心增加对话框交互，完善
审计页面运行时模型和元数据展示，补充单元测试。

server/src/app/services/employee_seed_part2.py

@@ -87,7 +87,7 @@ EMPLOYEE_DEFINITIONS_PART_2 = [
         "spotlight": True,
         "updated_at": "2026-05-07 09:52",
         "last_sync_at": "2026-05-07 09:52",
-        "role_codes": ["auditor", "finance"],
+        "role_codes": ["budget_monitor", "finance"],
         "history": [
             {
                 "action": "更新审计观察范围",
@@ -121,7 +121,7 @@ EMPLOYEE_DEFINITIONS_PART_2 = [
         "spotlight": False,
         "updated_at": "2026-05-07 08:58",
         "last_sync_at": "2026-05-07 08:40",
-        "role_codes": ["auditor"],
+        "role_codes": ["budget_monitor"],
     },
     {
         "employee_no": "E12688",
@@ -385,7 +385,7 @@ EMPLOYEE_DEFINITIONS_PART_2 = [
         "spotlight": False,
         "updated_at": "2026-05-03 13:18",
         "last_sync_at": "2026-05-03 13:18",
-        "role_codes": ["auditor"],
+        "role_codes": ["budget_monitor"],
     },
     {
         "employee_no": "E12790",
@@ -407,6 +407,6 @@ EMPLOYEE_DEFINITIONS_PART_2 = [
         "spotlight": False,
         "updated_at": "2026-05-06 08:56",
         "last_sync_at": "2026-05-06 08:56",
-        "role_codes": ["user", "auditor"],
+        "role_codes": ["user", "budget_monitor"],
     },
 ]