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/2024/truncate.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var floor = require('./floor');
+
+var $TypeError = require('es-errors/type');
+
+// https://262.ecma-international.org/14.0/#eqn-truncate
+
+module.exports = function truncate(x) {
+	if (typeof x !== 'number' && typeof x !== 'bigint') {
+		throw new $TypeError('argument must be a Number or a BigInt');
+	}
+	var result = x < 0 ? -floor(-x) : floor(x);
+	return result === 0 ? 0 : result; // in the spec, these are math values, so we filter out -0 here
+};