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/expense_claim_budget_flow.py

@@ -0,0 +1,96 @@
+from __future__ import annotations
+
+from typing import Any
+
+from app.api.deps import CurrentUserContext
+from app.models.financial_record import ExpenseClaim
+from app.services.budget import BudgetService
+
+
+class ExpenseClaimBudgetFlowMixin:
+    def _reserve_budget_for_submission(
+        self,
+        claim: ExpenseClaim,
+        current_user: CurrentUserContext,
+        *,
+        is_application_claim: bool,
+    ) -> list[dict[str, Any]]:
+        source_type = "application" if is_application_claim else "claim"
+        return BudgetService(self.db).reserve_for_claim(
+            claim,
+            source_type=source_type,
+            operator=self._resolve_budget_operator(current_user),
+        )
+
+    def _release_budget_for_return(
+        self,
+        claim: ExpenseClaim,
+        current_user: CurrentUserContext,
+        *,
+        reason: str,
+    ) -> list[dict[str, Any]]:
+        is_application_claim = self._is_expense_application_claim(claim)
+        source_type = "application" if is_application_claim else "claim"
+        return BudgetService(self.db).release_for_claim(
+            claim,
+            source_type=source_type,
+            operator=self._resolve_budget_operator(current_user),
+            reason=reason,
+        )
+
+    def _release_budget_for_delete(
+        self,
+        claim: ExpenseClaim,
+        current_user: CurrentUserContext,
+    ) -> None:
+        is_application_claim = self._is_expense_application_claim(claim)
+        source_type = "application" if is_application_claim else "claim"
+        BudgetService(self.db).release_for_claim(
+            claim,
+            source_type=source_type,
+            operator=self._resolve_budget_operator(current_user),
+            reason="单据删除释放预算预占",
+        )
+
+    def _consume_budget_for_finance_approval(
+        self,
+        claim: ExpenseClaim,
+        current_user: CurrentUserContext,
+    ) -> dict[str, Any] | None:
+        return BudgetService(self.db).consume_for_claim(
+            claim,
+            operator=self._resolve_budget_operator(current_user),
+            reason="财务终审通过核销预算",
+        )
+
+    def _transfer_application_budget_to_reimbursement(
+        self,
+        *,
+        application_claim: ExpenseClaim,
+        draft_claim: ExpenseClaim,
+        current_user: CurrentUserContext,
+    ) -> dict[str, Any] | None:
+        return BudgetService(self.db).transfer_application_reservation(
+            application_claim=application_claim,
+            draft_claim=draft_claim,
+            operator=self._resolve_budget_operator(current_user),
+        )
+
+    @staticmethod
+    def _append_budget_flags(
+        risk_flags: list[Any] | None,
+        budget_flags: list[dict[str, Any]] | dict[str, Any] | None,
+    ) -> list[Any]:
+        if budget_flags is None:
+            return list(risk_flags or [])
+        if isinstance(budget_flags, dict):
+            next_flags = [budget_flags]
+        else:
+            next_flags = list(budget_flags or [])
+        if not next_flags:
+            return list(risk_flags or [])
+        return [*list(risk_flags or []), *next_flags]
+
+    @staticmethod
+    def _resolve_budget_operator(current_user: CurrentUserContext) -> str:
+        return current_user.name or current_user.username or "system"