feat(pay): content cashier, resource orders at VIP price, purchase/download JS loop

Wire zibll-style one-shot points/cash cashier for post+_aksrt_pay downloads:
server amount from aksrt_get_user_pay_price, ORDER_PRODUCT_RESOURCE unlock,
frontend need-purchase opens modal, download box purchased/VIP/purchase CTAs.

inc/bootstrap.php

@@ -217,6 +217,9 @@ require_once AKSRT_DIR . '/inc/classes/class-aksrt-invite.php';
 // 加载下载服务（CMS / 资源 token 流程）
 require_once AKSRT_DIR . '/inc/classes/class-aksrt-download.php';
 
+// 付费内容收银台（post/_aksrt_pay → resource 订单）
+require_once AKSRT_DIR . '/inc/classes/class-aksrt-content-pay.php';
+
 // 下载状态统一解析器
 require_once AKSRT_DIR . '/inc/classes/class-aksrt-download-state.php';