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_part1.py

@@ -99,7 +99,7 @@ EMPLOYEE_DEFINITIONS_PART_1 = [
         "spotlight": False,
         "updated_at": "2026-05-07 09:35",
         "last_sync_at": "2026-05-07 09:10",
-        "role_codes": ["finance", "auditor"],
+        "role_codes": ["finance", "budget_monitor"],
     },
     {
         "employee_no": "E10289",
@@ -143,7 +143,7 @@ EMPLOYEE_DEFINITIONS_PART_1 = [
         "spotlight": False,
         "updated_at": "2026-05-05 09:18",
         "last_sync_at": "2026-05-05 09:18",
-        "role_codes": ["manager", "auditor"],
+        "role_codes": ["manager", "budget_monitor"],
     },
     {
         "employee_no": "E11618",
@@ -363,7 +363,7 @@ EMPLOYEE_DEFINITIONS_PART_1 = [
         "spotlight": False,
         "updated_at": "2026-05-06 13:08",
         "last_sync_at": "2026-05-06 13:08",
-        "role_codes": ["user", "approver", "auditor"],
+        "role_codes": ["user", "approver", "budget_monitor"],
     },
     {
         "employee_no": "E11991",