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/SchemaExtensions.php

@@ -0,0 +1,25 @@
+<?php
+/**
+ * @package AKSRT
+ */
+
+namespace AKSRT\Admin\Schema;
+
+defined('ABSPATH') || exit;
+
+class SchemaExtensions {
+
+    public static function build(): array {
+        return [
+            'domain'   => 'extensions',
+            'title'    => '扩展&增强',
+            'sections' => [
+                'ip'        => SchemaExtensionsIP::build(),
+                'audit'     => SchemaExtensionsAudit::build(),
+                'push'      => SchemaExtensionsPush::build(),
+                'security'  => SchemaExtensionsSecurity::build(),
+                'docs-mode' => SchemaExtensionsDocsMode::build(),
+            ],
+        ];
+    }
+}