fix(R56): 修复费用标准编辑时 expenseTypeId 校验失败

前端编辑提交时携带了只读字段 expenseTypeId，后端 strict schema 拒绝。
剔除只读字段后 PATCH 正常工作。

client/src/pages/ExpenseStandardsPage.tsx

@@ -140,8 +140,7 @@ export function ExpenseStandardsPage() {
 
   const saveMutation = useMutation({
     mutationFn: async () => {
-      const payload = {
-        expenseTypeId: form.expenseTypeId,
+      const mutablePayload = {
         name: form.name.trim(),
         maxAmount: form.maxAmount.trim(),
         perUnit: form.perUnit,
@@ -153,10 +152,13 @@ export function ExpenseStandardsPage() {
       };
 
       if (editingItem) {
-        return updateExpenseStandard(editingItem.id, payload);
+        return updateExpenseStandard(editingItem.id, mutablePayload);
       }
 
-      return createExpenseStandard(payload);
+      return createExpenseStandard({
+        expenseTypeId: form.expenseTypeId,
+        ...mutablePayload,
+      });
     },
     onSuccess: async () => {
       await queryClient.invalidateQueries({ queryKey: ["expense-standards"] });