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/package-lock.json

@@ -38,6 +38,7 @@
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                 "@types/react": "^18.3.5",
                 "@types/react-dom": "^18.3.0",
                 "@typescript-eslint/eslint-plugin": "^8.46.3",
@@ -2742,6 +2743,16 @@
             "dev": true,
             "license": "MIT"
         },
+        "node_modules/@types/node": {
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+            "resolved": "https://registry.npmjs.org/@types/node/-/node-22.19.1.tgz",
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+            "dev": true,
+            "license": "MIT",
+            "dependencies": {
+                "undici-types": "~6.21.0"
+            }
+        },
         "node_modules/@types/prop-types": {
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             "resolved": "https://registry.npmjs.org/@types/prop-types/-/prop-types-15.7.15.tgz",
@@ -7253,6 +7264,13 @@
                 "url": "https://github.com/sponsors/ljharb"
             }
         },
+        "node_modules/undici-types": {
+            "version": "6.21.0",
+            "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
+            "integrity": "sha512-iwDZqg0QAGrg9Rav5H4n0M64c3mkR59cJ6wQp+7C4nI0gsmExaedaYLNO44eT4AtBBwjbTiGPMlt2Md0T9H9JQ==",
+            "dev": true,
+            "license": "MIT"
+        },
         "node_modules/update-browserslist-db": {
             "version": "1.1.4",
             "resolved": "https://registry.npmjs.org/update-browserslist-db/-/update-browserslist-db-1.1.4.tgz",