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/@wordpress/priority-queue/README.md

@@ -0,0 +1,52 @@
+# Priority Queue
+
+This module allows you to run a queue of callback while on the browser's idle time making sure the higher-priority work is performed first.
+
+## Installation
+
+Install the module
+
+```bash
+npm install @wordpress/priority-queue --save
+```
+
+_This package assumes that your code will run in an **ES2015+** environment. If you're using an environment that has limited or no support for such language features and APIs, you should include [the polyfill shipped in `@wordpress/babel-preset-default`](https://github.com/WordPress/gutenberg/tree/HEAD/packages/babel-preset-default#polyfill) in your code._
+
+## API
+
+<!-- START TOKEN(Autogenerated API docs) -->
+
+### createQueue
+
+Creates a context-aware queue that only executes the last task of a given context.
+
+_Usage_
+
+```js
+import { createQueue } from '@wordpress/priority-queue';
+
+const queue = createQueue();
+
+// Context objects.
+const ctx1 = {};
+const ctx2 = {};
+
+// For a given context in the queue, only the last callback is executed.
+queue.add( ctx1, () => console.log( 'This will be printed first' ) );
+queue.add( ctx2, () => console.log( "This won't be printed" ) );
+queue.add( ctx2, () => console.log( 'This will be printed second' ) );
+```
+
+_Returns_
+
+-   `WPPriorityQueue`: Queue object with `add`, `flush` and `reset` methods.
+
+<!-- END TOKEN(Autogenerated API docs) -->
+
+## Contributing to this package
+
+This is an individual package that's part of the Gutenberg project. The project is organized as a monorepo. It's made up of multiple self-contained software packages, each with a specific purpose. The packages in this monorepo are published to [npm](https://www.npmjs.com/) and used by [WordPress](https://make.wordpress.org/core/) as well as other software projects.
+
+To find out more about contributing to this package or Gutenberg as a whole, please read the project's main [contributor guide](https://github.com/WordPress/gutenberg/tree/HEAD/CONTRIBUTING.md).
+
+<br /><br /><p align="center"><img src="https://s.w.org/style/images/codeispoetry.png?1" alt="Code is Poetry." /></p>