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-board.php

@@ -9,7 +9,7 @@ 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();
 $board = get_queried_object();
 $board_id = $board ? (int) $board->term_id : 0;
@@ -48,7 +48,7 @@ $board_url = !empty($board_data['url']) ? (string) $board_data['url'] : (is_wp_e
 $nonce = wp_create_nonce('aksrt_public_nonce');
 $max_pages = (int) ($view['pagination']['max_pages'] ?? 1);
 
-$forum_settings = class_exists('AKSRT_Settings') ? AKSRT_Settings::get_forum_settings() : [];
+$forum_settings = class_exists('\AKSRT\Settings\Settings') ? \AKSRT\Settings\Settings::get_forum_settings() : [];
 $forum_names = $forum_settings['names'] ?? [];
 $name_topic = $forum_names['posts'] ?? __('主题', 'aksrt');
 $name_reply = $forum_names['comment'] ?? __('回复', 'aksrt');