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/2023/InstallErrorCause.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var isObject = require('es-object-atoms/isObject');
+
+var CreateNonEnumerableDataPropertyOrThrow = require('./CreateNonEnumerableDataPropertyOrThrow');
+var Get = require('./Get');
+var HasProperty = require('./HasProperty');
+
+// https://262.ecma-international.org/13.0/#sec-installerrorcause
+
+module.exports = function InstallErrorCause(O, options) {
+	if (!isObject(O)) {
+		throw new $TypeError('Assertion failed: Type(O) is not Object');
+	}
+
+	if (isObject(options) && HasProperty(options, 'cause')) {
+		var cause = Get(options, 'cause');
+		CreateNonEnumerableDataPropertyOrThrow(O, 'cause', cause);
+	}
+};