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-snapshot/build/plugins.js

@@ -0,0 +1,43 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.getSerializers = exports.addSerializer = void 0;
+var _prettyFormat = require('pretty-format');
+var _mockSerializer = _interopRequireDefault(require('./mockSerializer'));
+function _interopRequireDefault(obj) {
+  return obj && obj.__esModule ? obj : {default: obj};
+}
+/**
+ * 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 {
+  DOMCollection,
+  DOMElement,
+  Immutable,
+  ReactElement,
+  ReactTestComponent,
+  AsymmetricMatcher
+} = _prettyFormat.plugins;
+let PLUGINS = [
+  ReactTestComponent,
+  ReactElement,
+  DOMElement,
+  DOMCollection,
+  Immutable,
+  _mockSerializer.default,
+  AsymmetricMatcher
+];
+
+// Prepend to list so the last added is the first tested.
+const addSerializer = plugin => {
+  PLUGINS = [plugin].concat(PLUGINS);
+};
+exports.addSerializer = addSerializer;
+const getSerializers = () => PLUGINS;
+exports.getSerializers = getSerializers;