完善借款、编号、付款与预算并发及验收（09-06-release-gate-integrity）

汇总已落盘的借款本金与还款、兼容历史编号的周期化编号、付款责任与回单核验、报销进度和排序、PWA/采购事务、错误原因与日期校验及ERP退役。
统一共享预算池锁序和锁后判断，恢复差旅原预算选择，补原因码固定夹具及反向完整性检查。
纳入配套迁移、测试、受管QA、分层验收合同、规约及任务记录；原始证据留在ignored artifacts。

关联任务：09-17-company-loan-principal-repayment、09-17-erp-exclusive-retirement、09-18-reimbursement-periodic-numbering、09-08-reimbursement-payment-closeout、09-18-local-concurrency-product-fixes、09-19-budget-pool-concurrency、09-05-error-explainability-payment-readiness。
预算补审由Claude定向验证2文件928项通过，原4446/28及r6结果仍仅对应各自历史输入；本轮未重跑测试。
完整新候选门禁、R1真实入口接入与12项公网义务仍开放。生产编号未启用、差旅仍冻结；不推送、不部署，不宣称发布资格。

server/tests/unit/services/payroll.month.test.js

@@ -0,0 +1,17 @@
+const { parsePayMonth } = require("../../../src/services/payroll");
+
+describe("pay month UTC boundaries", () => {
+  it.each([
+    ["2024-02", "2024-02-29T23:59:59.999Z"],
+    ["2026-02", "2026-02-28T23:59:59.999Z"],
+    ["2024-12", "2024-12-31T23:59:59.999Z"],
+  ])("keeps exact leap/month-end %s", (month, end) => {
+    const result = parsePayMonth(month);
+    expect(result.value).toBe(month);
+    expect(result.startDate.toISOString()).toBe(`${month}-01T00:00:00.000Z`);
+    expect(result.endDate.toISOString()).toBe(end);
+  });
+  it.each(["2026-00", "2026-13", "2026-1", "", undefined, null])("rejects invalid month %s", (input) => {
+    expect(parsePayMonth(input)).toBeNull();
+  });
+});