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/tests/unit/utils/date.test.js

@@ -0,0 +1,12 @@
+const { isValidDateOnlyString, parseDateOnlyString } = require("../../../src/utils/date");
+
+describe("strict calendar date validation", () => {
+  it.each(["2024-02-29", "2000-02-29", "2026-04-30", "2026-12-31", "0099-01-01"])("accepts %s without timezone shifts", (value) => {
+    expect(isValidDateOnlyString(value)).toBe(true);
+    expect(parseDateOnlyString(value).toISOString()).toBe(`${value}T00:00:00.000Z`);
+  });
+
+  it.each(["2026-02-30", "2026-02-29", "1900-02-29", "2026-04-31", "2026-13-01", "2026-00-01", "2026-01-00", "2026-01-32", "2026-1-01", " 2026-01-01", "2026-01-01T00:00:00Z", "", null, undefined, 20260101])("rejects invalid input %s", (value) => {
+    expect(isValidDateOnlyString(value)).toBe(false);
+  });
+});