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/jest-diff/build/constants.js

@@ -0,0 +1,19 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.SIMILAR_MESSAGE = exports.NO_DIFF_MESSAGE = void 0;
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const NO_DIFF_MESSAGE = 'Compared values have no visual difference.';
+exports.NO_DIFF_MESSAGE = NO_DIFF_MESSAGE;
+const SIMILAR_MESSAGE =
+  'Compared values serialize to the same structure.\n' +
+  'Printing internal object structure without calling `toJSON` instead.';
+exports.SIMILAR_MESSAGE = SIMILAR_MESSAGE;