feat(widgets): singular post pay purchase sidebar box

Add WidgetPostPayBox (zibll posts_pay parity) with theme skins,
paid/unpaid CTAs, sales badge, and registration.

inc/modules/widgets-register.php

@@ -81,6 +81,7 @@ function aksrt_register_widgets() {
 		register_widget('\AKSRT\Widgets\WidgetFeatureIntro');
 		register_widget('\AKSRT\Widgets\WidgetTermCards');
 		register_widget('\AKSRT\Widgets\WidgetPaidPosts');
+			register_widget('\AKSRT\Widgets\WidgetPostPayBox');
 		register_widget('\AKSRT\Widgets\WidgetAuthorCard');
 		register_widget('\AKSRT\Widgets\WidgetOnelinePosts');
 		register_widget('\AKSRT\Widgets\WidgetTiltCases');