fix(vip): 积分兑换弹窗改服务端渲染并与 Zibll 1:1 对齐

/user/vip/ 的积分兑换会员弹窗原先是前端自行拼装的，结构与层级都与参考主题
Zibll 不一致：Zibll 走 zibpay_get_vip_points_exchange_modal() 服务端渲染静态
壳，前端只按需开合。改为同一模型，前端不再拼 HTML。

- VipServiceModal 新增 get_points_exchange_modal_html()：门控（未登录/未开启
  返回空串）、vip-card 套餐选择、积分不足提示与提交表单；wp_footer 挂载输出
- pay-vip.js 移除 renderPointsModal / pointsPackage / exchangeFromModal /
  vipPointsPay，改为自包含开合（.in + 内联 display:flex + 独立遮罩 +
  body.modal-open + ESC），保留 aksrt-vip-points-toast 的 load/success/danger 契约
- 移除 /user/vip/ 页面底部独立积分兑换入口及其样式（uc-vip-points-link）
- credits.js 清理依赖全站不存在选择器的死代码 initVipPointsExchange()
- vip-modal.css 删除 71 行自实现样式，改为 .modal[data-aksrt-vip-points-modal]
  显隐契约；层级 100050 < 遮罩 100055 < 弹窗 100060 < notyf 10000000
- 新增 vip-points-exchange-modal 契约测试（7 项），toast-contract 同步

静止态必须显式 display:none，否则 .flex{display:flex} 会覆盖 .modal{display:none}
形成隐形遮罩拦截整页点击。

未写数据迁移。

验证：node --test tests/widget-system/*.test.cjs 308 项全部通过；php -l 全部
改动文件通过；隔离渲染桩确认积分充足 / 积分不足 / 功能关闭 / 未登录四种情形
的 HTML 产物正确。

assets/css/frontend/vip-modal.css

@@ -41,79 +41,28 @@
   position: relative;
 }
 
-.aksrt-vip-points-modal__title {
-  margin: 0 0 6px;
-  padding-right: 24px;
-  font-size: 20px;
-}
-.aksrt-vip-points-modal__desc,
-.aksrt-vip-points-modal__note {
-  margin: 0 0 12px;
-  color: var(--muted-color, #777);
-  font-size: 13px;
-  line-height: 1.6;
-}
-.aksrt-vip-points-modal__balance {
-  display: flex;
-  align-items: baseline;
-  justify-content: space-between;
-  gap: 12px;
-  margin: 0 0 14px;
-  padding: 12px 14px;
-  border: 1px solid rgba(16, 185, 129, 0.2);
-  border-radius: 10px;
-  background: rgba(16, 185, 129, 0.08);
-}
-.aksrt-vip-points-modal__balance-label { color: var(--muted-color, #777); font-size: 13px; }
-.aksrt-vip-points-modal__balance-value { color: #047857; font-size: 17px; }
-.aksrt-vip-points-modal__packages { display: grid; gap: 9px; margin-bottom: 14px; }
-.aksrt-vip-points-option { display: block; cursor: pointer; }
-.aksrt-vip-points-option > input {
-  position: absolute;
-  width: 1px;
-  height: 1px;
-  opacity: 0;
-}
-.aksrt-vip-points-option__card {
-  display: grid;
-  grid-template-columns: 1fr auto;
-  gap: 4px 10px;
-  padding: 12px 13px;
-  border: 1px solid var(--color-line, rgba(0, 0, 0, 0.1));
-  border-radius: 10px;
-  background: var(--main-bg-color, #fff);
-  transition: border-color .15s ease, box-shadow .15s ease;
-}
-.aksrt-vip-points-option__title { font-size: 14px; }
-.aksrt-vip-points-option__days { color: var(--muted-color, #777); font-size: 12px; }
-.aksrt-vip-points-option__cost { grid-row: 1 / span 2; grid-column: 2; align-self: center; color: #047857; font-size: 14px; font-weight: 700; }
-.aksrt-vip-points-option > input:checked + .aksrt-vip-points-option__card {
-  border-color: #10b981;
-  box-shadow: 0 0 0 2px rgba(16, 185, 129, 0.14);
-}
-.aksrt-vip-points-option > input:focus-visible + .aksrt-vip-points-option__card { outline: 3px solid rgba(16, 185, 129, 0.3); outline-offset: 2px; }
-.aksrt-vip-points-option.is-disabled { cursor: not-allowed; opacity: .55; }
-.aksrt-vip-points-option.is-disabled .aksrt-vip-points-option__cost { color: #b91c1c; }
-.aksrt-vip-points-modal__empty { padding: 22px 12px; color: var(--muted-color, #777); text-align: center; }
-.aksrt-vip-points-submit {
-  width: 100%;
-  min-height: 42px;
-  border: 0;
-  border-radius: 999px;
-  color: #fff;
-  background: linear-gradient(90deg, #059669, #10b981);
-  cursor: pointer;
-  font: inherit;
-  font-weight: 700;
-}
-.aksrt-vip-points-submit:disabled { cursor: not-allowed; opacity: .5; }
-.aksrt-vip-points-submit.is-loading { cursor: wait; opacity: .7; }
-.aksrt-vip-points-modal__tip { min-height: 1.4em; margin: 9px 0 0; }
-@media (max-width: 480px) {
-  .aksrt-vip-points-modal { padding: 16px 13px 14px; }
-  .aksrt-vip-points-modal__balance { align-items: flex-start; flex-direction: column; gap: 3px; }
+/* 积分兑换会员弹窗：参考主题 refresh_modal 同构静态壳
+   （.modal.flex.jc.fade > .modal-dialog.modal-mini.full-sm > .modal-content
+   > .modal-body，由 inc/helpers/aksrt-vip.php 服务端输出）。三点约束：
+   - 静止态必须显式隐藏：main.css 的 .flex{display:flex}（后加载、与 bootstrap
+     的 .modal{display:none} 同特异性）会让壳永久铺满全屏，叠加 .fade 的
+     opacity:0 形成隐形遮罩，拦截整页点击；
+   - 打开态由 pay-vip.js 自包含开关的内联 display:flex 驱动（block 会破坏
+     .flex.jc 双轴居中），与余额充值/购买积分弹窗同构；
+   - 入口在本页 runtime 会员弹窗内，壳需高于 runtime 宿主（100050），以复现
+     参考主题在会员弹窗之上再叠一层兑换弹窗的行为。 */
+.modal[data-aksrt-vip-points-modal] {
+  display: none;
+  z-index: 100060;
 }
 
+.modal[data-aksrt-vip-points-modal].in {
+  display: flex;
+}
+
+.modal-backdrop[data-aksrt-vip-points-backdrop] {
+  z-index: 100055;
+}
 
 .pay-vip-form-row {
   display: grid;