fix(admin): register REST controllers via FQCN after PSR-4

Admin::register_rest_routes used bare class strings like
'GlobalController', so class_exists() failed after the namespace move
and no aksrt/v1 settings/banner/schema routes registered (SPA 404).

src/AKSRT/Admin/Admin.php

@@ -171,21 +171,22 @@ class Admin {
     }
 
     public function register_rest_routes(): void {
+        // FQCN required after PSR-4 move into AKSRT\Admin (unqualified class_exists skips all routes).
         $controllers = [
-            'GlobalController',
-            'PageDisplayController',
-            'PostListController',
-            'PermissionsController',
-            'UserController',
-            'PaymentController',
-            'ToolsController',
-            'ImportExportController',
-            'ShopController',
-            'ForumController',
-            'ExtensionController',
-            'CommentController',
-            'MessageController',
-            'AIController',
+            GlobalController::class,
+            PageDisplayController::class,
+            PostListController::class,
+            PermissionsController::class,
+            UserController::class,
+            PaymentController::class,
+            ToolsController::class,
+            ImportExportController::class,
+            ShopController::class,
+            ForumController::class,
+            ExtensionController::class,
+            CommentController::class,
+            MessageController::class,
+            AIController::class,
         ];
 
         foreach ($controllers as $class_name) {