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/lib/api/client.ts

@@ -88,35 +88,44 @@ class ApiClient {
   }
 }
 
-// Export singleton instance
-export const api = new ApiClient();
-
-// Export API endpoints
-export const endpoints = {
-  // Shop
-  products: '/shop/products',
-  product: (id: number) => `/shop/products/${id}`,
-  categories: '/shop/categories',
-  search: '/shop/search',
-  
-  // Cart
-  cart: '/cart',
-  cartAdd: '/cart/add',
-  cartUpdate: '/cart/update',
-  cartRemove: '/cart/remove',
-  cartCoupon: '/cart/apply-coupon',
-  
-  // Checkout
-  checkoutCalculate: '/checkout/calculate',
-  checkoutCreate: '/checkout/create-order',
-  paymentMethods: '/checkout/payment-methods',
-  shippingMethods: '/checkout/shipping-methods',
-  
-  // Account
-  orders: '/account/orders',
-  order: (id: number) => `/account/orders/${id}`,
-  downloads: '/account/downloads',
-  profile: '/account/profile',
-  password: '/account/password',
-  addresses: '/account/addresses',
+// API endpoints
+const endpoints = {
+  shop: {
+    products: '/shop/products',
+    product: (id: number) => `/shop/products/${id}`,
+    categories: '/shop/categories',
+    search: '/shop/search',
+  },
+  cart: {
+    get: '/cart',
+    add: '/cart/add',
+    update: '/cart/update',
+    remove: '/cart/remove',
+    applyCoupon: '/cart/apply-coupon',
+    removeCoupon: '/cart/remove-coupon',
+  },
+  checkout: {
+    calculate: '/checkout/calculate',
+    create: '/checkout/create-order',
+    paymentMethods: '/checkout/payment-methods',
+    shippingMethods: '/checkout/shipping-methods',
+  },
+  account: {
+    orders: '/account/orders',
+    order: (id: number) => `/account/orders/${id}`,
+    downloads: '/account/downloads',
+    profile: '/account/profile',
+    password: '/account/password',
+    addresses: '/account/addresses',
+  },
 };
+
+// Create singleton instance with endpoints
+const client = new ApiClient();
+
+// Export as apiClient with endpoints attached
+export const apiClient = Object.assign(client, { endpoints });
+
+// Also export individual pieces for convenience
+export const api = client;
+export { endpoints };