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-util/build/ErrorWithStack.js

@@ -0,0 +1,28 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.default = 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.
+ */
+
+class ErrorWithStack extends Error {
+  constructor(message, callsite, stackLimit) {
+    // Ensure we have a large stack length so we get full details.
+    const originalStackLimit = Error.stackTraceLimit;
+    if (stackLimit) {
+      Error.stackTraceLimit = Math.max(stackLimit, originalStackLimit || 10);
+    }
+    super(message);
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this, callsite);
+    }
+    Error.stackTraceLimit = originalStackLimit;
+  }
+}
+exports.default = ErrorWithStack;