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/NumberToBigInt.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $BigInt = GetIntrinsic('%BigInt%', true);
+var $RangeError = require('es-errors/range');
+var $SyntaxError = require('es-errors/syntax');
+var $TypeError = require('es-errors/type');
+
+var isInteger = require('math-intrinsics/isInteger');
+
+// https://262.ecma-international.org/12.0/#sec-numbertobigint
+
+module.exports = function NumberToBigInt(number) {
+	if (typeof number !== 'number') {
+		throw new $TypeError('Assertion failed: `number` must be a String');
+	}
+	if (!isInteger(number)) {
+		throw new $RangeError('The number ' + number + ' cannot be converted to a BigInt because it is not an integer');
+	}
+	if (!$BigInt) {
+		throw new $SyntaxError('BigInts are not supported in this environment');
+	}
+	return $BigInt(number);
+};