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/2020/OrdinaryCreateFromConstructor.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+var $TypeError = require('es-errors/type');
+
+var GetPrototypeFromConstructor = require('./GetPrototypeFromConstructor');
+var IsArray = require('./IsArray');
+var OrdinaryObjectCreate = require('./OrdinaryObjectCreate');
+
+// https://262.ecma-international.org/6.0/#sec-ordinarycreatefromconstructor
+
+module.exports = function OrdinaryCreateFromConstructor(constructor, intrinsicDefaultProto) {
+	GetIntrinsic(intrinsicDefaultProto); // throws if not a valid intrinsic
+	var proto = GetPrototypeFromConstructor(constructor, intrinsicDefaultProto);
+	var slots = arguments.length < 3 ? [] : arguments[2];
+	if (!IsArray(slots)) {
+		throw new $TypeError('Assertion failed: if provided, `internalSlotsList` must be a List');
+	}
+	return OrdinaryObjectCreate(proto, slots);
+};