refactor: flatten src/AKSRT → src (drop theme-identifier dir)

Move all domain folders from src/AKSRT/{Domain} to src/{Domain}; remap
Composer PSR-4 "AKSRT\\": "src/"; update audit script + README + ADR
paths; remove dead tools/build-psr4-map.php (scanned deleted inc/classes).

src/Admin/Schema/SchemaToolsBackup.php

@@ -0,0 +1,32 @@
+<?php
+/**
+ * @package AKSRT
+ */
+
+namespace AKSRT\Admin\Schema;
+
+defined('ABSPATH') || exit;
+
+class SchemaToolsBackup {
+
+    public static function build(): array {
+        return [
+            'key'        => 'backup',
+            'title'      => '数据备份',
+            'version'    => '1.0.0',
+            'option_key' => 'aksrt_settings',
+            'groups'     => [
+                ['key' => 'backup', 'title' => '备份设置', 'fields' => [
+                    ['key' => 'backup_auto', 'label' => '自动备份', 'type' => 'switch', 'help' => '启用自动定时备份'],
+                    ['key' => 'backup_frequency', 'label' => '备份频率', 'type' => 'select', 'default' => 'weekly', 'options' => [
+                        ['label' => '每天', 'value' => 'daily'],
+                        ['label' => '每周', 'value' => 'weekly'],
+                        ['label' => '每月', 'value' => 'monthly'],
+                    ]],
+                    ['key' => 'backup_retain', 'label' => '保留份数', 'type' => 'number', 'default' => 7, 'min' => 3, 'max' => 20],
+                    ['key' => 'backup_now', 'label' => '立即备份', 'type' => 'button', 'help' => '手动触发一次完整备份'],
+                ]],
+            ],
+        ];
+    }
+}