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/models/__init__.py

@@ -3,6 +3,7 @@ from app.models.agent_asset import AgentAsset, AgentAssetReview, AgentAssetVersi
 from app.models.agent_run import AgentRun, AgentToolCall, SemanticParseLog
 from app.models.approval import ApprovalRecord
 from app.models.audit_log import AuditLog
+from app.models.budget import BudgetAllocation, BudgetReservation, BudgetTransaction
 from app.models.employee_change_log import EmployeeChangeLog
 from app.models.employee import Employee
 from app.models.financial_record import (
@@ -32,6 +33,9 @@ __all__ = [
     "AgentToolCall",
     "ApprovalRecord",
     "AuditLog",
+    "BudgetAllocation",
+    "BudgetReservation",
+    "BudgetTransaction",
     "Employee",
     "EmployeeChangeLog",
     "ExpenseClaim",