fix: 加固日历日期与动态错误合同（09-05-error-explainability-payment-readiness，09-08-reimbursement-payment-closeout）

server/src/utils/date.js

@@ -17,8 +17,15 @@ function parseDateOnlyString(value) {
   return new Date(`${value}T00:00:00.000Z`);
 }
 
+function isValidDateOnlyString(value) {
+  if (typeof value !== "string" || !/^\d{4}-\d{2}-\d{2}$/.test(value)) return false;
+  const date = parseDateOnlyString(value);
+  return Number.isFinite(date.getTime()) && date.toISOString().slice(0, 10) === value;
+}
+
 module.exports = {
   compactDateString,
   currentDateString,
   parseDateOnlyString,
+  isValidDateOnlyString,
 };