refactor(classes): organize inc/classes into domain folders

Move ~94 root class shells and root *-traits into domain directories
(core, auth, user, credits, content, payment/gateways, forum, shop,
sms, ai, messages, extensions, widgets, settings, admin). Update
bootstrap require paths, co-locate traits with owners, fix forum/user
relative requires, drop duplicate shop controller requires, and wire
home-modules load. Path-only; class names and init order unchanged.

slim-forum.php

@@ -3,7 +3,7 @@
  * Script to replace method bodies with delegation stubs in class-aksrt-forum.php
  */
 
-$file = __DIR__ . '/inc/classes/class-aksrt-forum.php';
+$file = __DIR__ . '/inc/classes/forum/class-aksrt-forum.php';
 $content = file_get_contents($file);
 if ($content === false) {
     echo "ERROR: Cannot read file\n";