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.

templates/pages/page-forums.php

@@ -12,7 +12,7 @@ defined('ABSPATH') || exit;
 
 get_header();
 
-$forum = class_exists('AKSRT_Forum') ? AKSRT_Forum::get_instance() : null;
+$forum = class_exists('\AKSRT\Forum\Forum') ? \AKSRT\Forum\Forum::get_instance() : null;
 $current_user_id = get_current_user_id();
 $view = $forum ? $forum->get_home_view($current_user_id) : [
     'boards' => [],
@@ -36,7 +36,7 @@ $permissions = $view['permissions'] ?? [];
 $applications = $view['applications'] ?? [];
 $compose_url = aksrt_get_forum_compose_url();
 
-$forum_settings = class_exists('AKSRT_Settings') ? AKSRT_Settings::get_forum_settings() : [];
+$forum_settings = class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_forum_settings() : [];
 $forum_names = $forum_settings['names'] ?? [];
 $name_forum = $forum_names['forum'] ?? __('论坛', 'aksrt');
 $name_plate = $forum_names['plate'] ?? __('版块', 'aksrt');