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-iterator-helpers/Iterator.from/shim.js

@@ -0,0 +1,18 @@
+'use strict';
+
+var getPolyfill = require('./polyfill');
+var define = require('define-properties');
+
+var getIteratorPolyfill = require('../Iterator/polyfill');
+
+module.exports = function shimIteratorFrom() {
+	var $Iterator = getIteratorPolyfill();
+	var polyfill = getPolyfill();
+	define(
+		$Iterator,
+		{ from: polyfill },
+		{ from: function () { return $Iterator.from !== polyfill; } }
+	);
+
+	return polyfill;
+};