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/forum/forum-compose.php

@@ -18,7 +18,7 @@ if (!is_user_logged_in()) {
     exit;
 }
 
-$forum = class_exists('AKSRT_Forum') ? AKSRT_Forum::get_instance() : null;
+$forum = class_exists('\AKSRT\Forum\Forum') ? \AKSRT\Forum\Forum::get_instance() : null;
 $current_user_id = get_current_user_id();
 $board_id = isset($_GET['board']) ? (int) $_GET['board'] : 0;
 $draft_id = isset($_GET['draft']) ? (int) $_GET['draft'] : 0;
@@ -33,7 +33,7 @@ $view = $forum ? $forum->get_compose_view($current_user_id, ['board_id' => $boar
     'capabilities' => [],
 ];
 
-$forum_settings = class_exists('AKSRT_Settings') ? AKSRT_Settings::get_forum_settings() : [];
+$forum_settings = class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_forum_settings() : [];
 $title_placeholder = $forum_settings['other']['t_placeholder'] ?? __('请输入标题', 'aksrt');
 $content_placeholder = $forum_settings['other']['c_placeholder'] ?? __('请输入内容', 'aksrt');
 $title_maxlen = max(5, min(100, (int) ($forum_settings['other']['title_strlen_limit'] ?? 30)));