fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

node_modules/@wordpress/url/build-module/prepend-https.js

@@ -0,0 +1,32 @@
+/**
+ * Internal dependencies
+ */
+import { prependHTTP } from './prepend-http';
+
+/**
+ * Prepends "https://" to a url, if it looks like something that is meant to be a TLD.
+ *
+ * Note: this will not replace "http://" with "https://".
+ *
+ * @param {string} url The URL to test.
+ *
+ * @example
+ * ```js
+ * const actualURL = prependHTTPS( 'wordpress.org' ); // https://wordpress.org
+ * ```
+ *
+ * @return {string} The updated URL.
+ */
+export function prependHTTPS(url) {
+  if (!url) {
+    return url;
+  }
+
+  // If url starts with http://, return it as is.
+  if (url.startsWith('http://')) {
+    return url;
+  }
+  url = prependHTTP(url);
+  return url.replace(/^http:/, 'https:');
+}
+//# sourceMappingURL=prepend-https.js.map