refactor(autoload): migrate theme classes to Composer PSR-4

Move 288 types from global AKSRT_* + inc/classes manual requires into
namespace AKSRT\{Domain} under src/AKSRT/, wire composer.json psr-4,
and slim bootstrap to helpers/modules/hooks only. Split multi-class
widget/gateway files, update admin contract audit paths, and document
the layout in ADR/README.

inc/helpers/menu-decoration.php

@@ -11,7 +11,7 @@
 defined('ABSPATH') || exit;
 
 /**
- * Get menu decoration settings from AKSRT_Settings.
+ * Get menu decoration settings from \AKSRT\Settings\Settings.
  *
  * @return array
  */
@@ -21,8 +21,8 @@ function aksrt_get_menu_decoration_settings(): array {
         return $cache;
     }
 
-    if (class_exists('AKSRT_Settings')) {
-        $all = AKSRT_Settings::get_all();
+    if (class_exists('\AKSRT\Settings\Settings')) {
+        $all = \AKSRT\Settings\Settings::get_all();
     } else {
         $all = [];
     }