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/core-js/modules/es.array.from.js

@@ -0,0 +1,15 @@
+'use strict';
+var $ = require('../internals/export');
+var from = require('../internals/array-from');
+var checkCorrectnessOfIteration = require('../internals/check-correctness-of-iteration');
+
+var INCORRECT_ITERATION = !checkCorrectnessOfIteration(function (iterable) {
+  // eslint-disable-next-line es/no-array-from -- required for testing
+  Array.from(iterable);
+});
+
+// `Array.from` method
+// https://tc39.es/ecma262/#sec-array.from
+$({ target: 'Array', stat: true, forced: INCORRECT_ITERATION }, {
+  from: from
+});