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.

functions.php

@@ -174,6 +174,9 @@ if (class_exists('AKSRT_Creator_Revenue')) {
 if (class_exists('AKSRT_Download')) {
     AKSRT_Download::get_instance()->init();
 }
+if (class_exists('AKSRT_Content_Pay')) {
+    AKSRT_Content_Pay::get_instance()->init();
+}
 // Download State & Docs Presenter are pure service singletons (no hooks)
 if (class_exists('AKSRT_Download_State')) {
     AKSRT_Download_State::get_instance();