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/user-center-renderers/credits-signin.php

@@ -23,8 +23,8 @@ if (function_exists('aksrt_is_captcha_enabled_for') && aksrt_is_captcha_enabled_
 endif;
 
 $signin_dates = [];
-if (class_exists('AKSRT_Signin')) {
-	$signin_log = AKSRT_Signin::get_instance()->get_recent_signins($user_id, 30);
+if (class_exists('\AKSRT\Credits\Signin')) {
+	$signin_log = \AKSRT\Credits\Signin::get_instance()->get_recent_signins($user_id, 30);
 	$signin_dates = array_filter(array_map(static function ($entry) {
 		return $entry['signin_date'] ?? '';
 	}, $signin_log));