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

admin-spa/src/App.tsx

@@ -214,6 +214,7 @@ import PushConfiguration from '@/routes/Settings/Notifications/PushConfiguration
 import EmailCustomization from '@/routes/Settings/Notifications/EmailCustomization';
 import EditTemplate from '@/routes/Settings/Notifications/EditTemplate';
 import SettingsDeveloper from '@/routes/Settings/Developer';
+import SettingsCustomerSPA from '@/routes/Settings/CustomerSPA';
 import MorePage from '@/routes/More';
 
 // Addon Route Component - Dynamically loads addon components
@@ -511,6 +512,7 @@ function AppRoutes() {
       <Route path="/settings/notifications/email-customization" element={<EmailCustomization />} />
       <Route path="/settings/notifications/edit-template" element={<EditTemplate />} />
       <Route path="/settings/brand" element={<SettingsIndex />} />
+      <Route path="/settings/customer-spa" element={<SettingsCustomerSPA />} />
       <Route path="/settings/developer" element={<SettingsDeveloper />} />
 
       {/* Dynamic Addon Routes */}