feat(admin): add native 支付中心 menu with orders/withdraw/cards (Phase 2a)

Introduce AKSRT_Admin_Pay_Menus as a zibll-style top-level WP admin shell
for payment ops. Overview, orders, withdrawals, and charge cards are
usable PHP list pages reusing Order_Repository / Withdrawal / Charge_Card.
Shipping, after-sale, coupons, income, and rebate are stubbed with SPA
fallback until Phase 2b.

functions.php

@@ -322,6 +322,11 @@ if (class_exists('AKSRT_User_Credits_Admin')) {
     AKSRT_User_Credits_Admin::get_instance()->init();
 }
 
+// WordPress 原生侧栏：支付/订单运营中心（zibll zibpay 对齐）
+if (is_admin() && class_exists('AKSRT_Admin_Pay_Menus')) {
+    AKSRT_Admin_Pay_Menus::get_instance()->init();
+}
+
 // ============================================================
 // 主题删除时的数据库清理（仅在用户启用清理选项时生效）
 // uninstall.php 会检查 aksrt_cleanup_on_uninstall 选项