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/@webpack-cli/configtest/README.md

@@ -0,0 +1,31 @@
+# webpack-cli configtest
+
+[![NPM Downloads][downloads]][downloads-url]
+
+> **Note**
+>
+> This package is used by webpack-cli under-the-hood and is not intended for installation
+
+## Description
+
+This package validates a webpack configuration.
+
+## Installation
+
+```bash
+#npm
+npm i -D @webpack-cli/configtest
+
+#yarn
+yarn add -D @webpack-cli/configtest
+
+```
+
+## Usage
+
+```bash
+npx webpack configtest [config-path]
+```
+
+[downloads]: https://img.shields.io/npm/dm/@webpack-cli/configtest.svg
+[downloads-url]: https://www.npmjs.com/package/@webpack-cli/configtest