feat(shop): add product taxonomy write REST for editor

Expose POST /shop/products/taxonomy to create category/tag terms,
enrich GET term payload with slug/parent/count, and let
ProductEditorDrawer create categories and ensure tags without WP
native UI.

inc/classes/admin/class-aksrt-admin-shop-controller.php

@@ -175,6 +175,13 @@ class AKSRT_Admin_Shop_Controller extends AKSRT_Admin_Controller_Base {
             'permission_callback' => [$this, 'check_permission'],
         ]);
 
+        // Create product category or tag term for the product editor.
+        register_rest_route(self::API_NAMESPACE, '/shop/products/taxonomy', [
+            'methods'             => 'POST',
+            'callback'            => [$this, 'create_product_taxonomy_term'],
+            'permission_callback' => [$this, 'check_permission'],
+        ]);
+
         // Product list
         register_rest_route(self::API_NAMESPACE, '/shop/products', [
             'methods'             => 'GET',