feat(widgets): simplify locations and paid sidebar

Remove deprecated widget locations and widgets, standardize sidebar labels, and render a compact paid-post purchase card in the article sidebar.

assets/js/page-template.js

@@ -26,9 +26,9 @@
       document.querySelector('[data-nav="posts"]') ||
       document.querySelector('[data-nav]');
 
-    // Support multiple TOC shells (built-in single sidebar + WidgetPostsNavs).
+    // The article sidebar and mobile drawer share one built-in TOC source.
     var tocWidgets = Array.prototype.slice.call(
-      document.querySelectorAll('.posts-nav-box.toc-widget, .posts-nav-box[data-title]')
+      document.querySelectorAll('.posts-nav-box.toc-widget')
     );
     var tocLists = [];
     tocWidgets.forEach(function (box) {