feat(vip): skeleton loading state and faster modal/site startup

The VIP purchase/renew modal opened with a single "loading..." line, which
reads as a hang while /pay/vip/modal round-trips. Every frontend pageview
also paid an option write inside wp_head, and the header user-card CSS was
enqueued even for guests who never see the card.

pay-vip.js now builds a full-layout skeleton (user box, level tabs, the
two-column package panel) from vipSkeleton(), reusing the global
aksrt-modal-runtime__skeleton line/block classes; the VIP-specific shapes
live in the conditionally loaded vip-modal.css, and the 640px two-column
threshold matches .pay-vip-form-row. The modal cache TTL goes 15s -> 60s
(purchase, card-pass redeem and points exchange already invalidate the
vip tag), and hover/focus on a .pay-vip trigger now prefetches the payload
through the same cacheKey and flight openRemote uses, so a warm click
opens instantly.

The bottom note and the whole help_text pipeline behind it are removed; the
admin-editable pay_user_vip_desc still renders at the top of the modal, and
the recharge/gateway help_text keys are untouched. get_catalog() reads
points and wallet balance through one new LedgerService::points_and_balance()
call. The StatsTracker counter write moves to shutdown so wp_head only does
the visitor check and setcookie, and header-userbox.css is enqueued for
logged-in users only.

Verification: node --test across the suite (628 tests, including the 7 new
contract assertions in tests/widget-system/vip-modal-skeleton.test.cjs) and
php -l on every changed PHP file. No visual acceptance performed, per request.

src/Core/ScriptsPart1b.php

@@ -63,7 +63,10 @@ trait ScriptsPart1b {
         };
 
         // 顶部导航用户卡片（legacy header-userbox 模块样式）。
-        $enqueue_module('header-userbox');
+        // 仅登录用户渲染用户卡（aksrt-header-userbox.php 的渲染条件），访客页面不加载。
+        if (is_user_logged_in()) {
+            $enqueue_module('header-userbox');
+        }
 
 		if (!is_user_logged_in() || (bool) get_query_var('aksrt_sign')) {
 			$auth_css = get_template_directory() . '/assets/css/routes/sign.css';