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/2022/MakeDate.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var $isFinite = require('math-intrinsics/isFinite');
+
+var msPerDay = require('../helpers/timeConstants').msPerDay;
+
+// https://262.ecma-international.org/5.1/#sec-15.9.1.13
+
+module.exports = function MakeDate(day, time) {
+	if (!$isFinite(day) || !$isFinite(time)) {
+		return NaN;
+	}
+	return (day * msPerDay) + time;
+};