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/array-includes/implementation.js

@@ -0,0 +1,36 @@
+'use strict';
+
+var ToIntegerOrInfinity = require('es-abstract/2025/ToIntegerOrInfinity');
+var ToLength = require('es-abstract/2025/ToLength');
+var ToObject = require('es-object-atoms/ToObject');
+var SameValueZero = require('es-abstract/2025/SameValueZero');
+var $isNaN = require('math-intrinsics/isNaN');
+var $isFinite = require('math-intrinsics/isFinite');
+var GetIntrinsic = require('get-intrinsic');
+var callBound = require('call-bound');
+var isString = require('is-string');
+
+var $charAt = callBound('String.prototype.charAt');
+var $indexOf = GetIntrinsic('%Array.prototype.indexOf%'); // TODO: use callBind.apply without breaking IE 8
+var $max = GetIntrinsic('%Math.max%');
+
+module.exports = function includes(searchElement) {
+	var fromIndex = arguments.length > 1 ? ToIntegerOrInfinity(arguments[1]) : 0;
+	if ($indexOf && !$isNaN(searchElement) && $isFinite(fromIndex) && typeof searchElement !== 'undefined') {
+		return $indexOf.apply(this, arguments) > -1;
+	}
+
+	var O = ToObject(this);
+	var length = ToLength(O.length);
+	if (length === 0) {
+		return false;
+	}
+	var k = fromIndex >= 0 ? fromIndex : $max(0, length + fromIndex);
+	while (k < length) {
+		if (SameValueZero(searchElement, isString(O) ? $charAt(O, k) : O[k])) {
+			return true;
+		}
+		k += 1;
+	}
+	return false;
+};