feat(shop): product editor SKU variants UI

Wire ProductEditorDrawer to existing /shop/products/{id}/variants REST
for list/save. Support attribute text parsing, batch replace save, and
optional save-variants-only. Align save endpoint JSON body parsing with
controller helper.

inc/classes/admin/class-aksrt-admin-shop-controller-variant-export-operations.php

@@ -31,7 +31,9 @@ trait AKSRT_Admin_Shop_Controller_Variant_Export_Operations {
             return $this->error('商品不存在', 404);
         }
 
-        $params = $request->get_json_params() ?? [];
+        $params = method_exists($this, 'get_json_params')
+            ? $this->get_json_params($request)
+            : ($request->get_json_params() ?? []);
         $variants = $params['variants'] ?? [];
         if (!is_array($variants)) {
             return $this->error('变体数据格式错误');