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.

src/AKSRT/Admin/Schema/SchemaForumUpload.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * @package AKSRT
+ */
+
+namespace AKSRT\Admin\Schema;
+
+defined('ABSPATH') || exit;
+
+class SchemaForumUpload {
+
+    public static function build(): array {
+        return [
+            'key'        => 'upload',
+            'title'      => '上传权限',
+            'version'    => '1.0.0',
+            'option_key' => 'aksrt_settings',
+            'groups'     => [
+                ['key' => 'limits', 'title' => '上传限制', 'fields' => [
+                    ['key' => 'bbs_upload_img_size', 'label' => '图片大小 (KB)', 'type' => 'number', 'default' => 2048, 'min' => 100],
+                    ['key' => 'bbs_image_upload_multiple', 'label' => '批量上传数', 'type' => 'number', 'default' => 9, 'min' => 1, 'max' => 20],
+                    ['key' => 'bbs_upload_video_size', 'label' => '视频大小 (KB)', 'type' => 'number', 'default' => 20480, 'min' => 1024],
+                    ['key' => 'bbs_upload_file_size', 'label' => '文件大小 (KB)', 'type' => 'number', 'default' => 10240, 'min' => 100],
+                    ['key' => 'bbs_upload_file_mimes', 'label' => '允许格式', 'type' => 'text', 'default' => 'jpg,jpeg,png,gif,mp4,zip,rar,pdf', 'help' => '逗号分隔'],
+                ]],
+            ],
+        ];
+    }
+}