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/es-abstract/helpers/IsArray.js

@@ -0,0 +1,12 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $Array = GetIntrinsic('%Array%');
+
+// eslint-disable-next-line global-require
+var toStr = !$Array.isArray && require('call-bound')('Object.prototype.toString');
+
+module.exports = $Array.isArray || function IsArray(argument) {
+	return toStr(argument) === '[object Array]';
+};