feat: Add product images support with WP Media Library integration

- Add WP Media Library integration for product and variation images
- Support images array (URLs) conversion to attachment IDs
- Add images array to API responses (Admin & Customer SPA)
- Implement drag-and-drop sortable images in Admin product form
- Add image gallery thumbnails in Customer SPA product page
- Initialize WooCommerce session for guest cart operations
- Fix product variations and attributes display in Customer SPA
- Add variation image field in Admin SPA

Changes:
- includes/Api/ProductsController.php: Handle images array, add to responses
- includes/Frontend/ShopController.php: Add images array for customer SPA
- includes/Frontend/CartController.php: Initialize WC session for guests
- admin-spa/src/lib/wp-media.ts: Add openWPMediaGallery function
- admin-spa/src/routes/Products/partials/tabs/GeneralTab.tsx: WP Media + sortable images
- admin-spa/src/routes/Products/partials/tabs/VariationsTab.tsx: Add variation image field
- customer-spa/src/pages/Product/index.tsx: Add gallery thumbnails display

customer-spa/src/components/Layout/Container.tsx

@@ -0,0 +1,15 @@
+import React from 'react';
+import { cn } from '@/lib/utils';
+
+interface ContainerProps {
+  children: React.ReactNode;
+  className?: string;
+}
+
+export default function Container({ children, className }: ContainerProps) {
+  return (
+    <div className={cn('container-safe py-8', className)}>
+      {children}
+    </div>
+  );
+}