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/IsValidIntegerIndex.js

@@ -0,0 +1,30 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var isNegativeZero = require('math-intrinsics/isNegativeZero');
+
+var IsDetachedBuffer = require('./IsDetachedBuffer');
+
+var isInteger = require('math-intrinsics/isInteger');
+var typedArrayBuffer = require('typed-array-buffer');
+
+// https://262.ecma-international.org/12.0/#sec-isvalidintegerindex
+
+module.exports = function IsValidIntegerIndex(O, index) {
+	// Assert: O is an Integer-Indexed exotic object.
+	var buffer = typedArrayBuffer(O); // step 1
+
+	if (typeof index !== 'number') {
+		throw new $TypeError('Assertion failed: Type(index) is not Number');
+	}
+
+	if (IsDetachedBuffer(buffer)) { return false; } // step 2
+
+	if (!isInteger(index)) { return false; } // step 3
+
+	if (isNegativeZero(index)) { return false; } // step 4
+
+	if (index < 0 || index >= O.length) { return false; } // step 5
+
+	return true; // step 6
+};