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/is-docker/readme.md

@@ -0,0 +1,27 @@
+# is-docker
+
+> Check if the process is running inside a Docker container
+
+## Install
+
+```
+$ npm install is-docker
+```
+
+## Usage
+
+```js
+const isDocker = require('is-docker');
+
+if (isDocker()) {
+	console.log('Running inside a Docker container');
+}
+```
+
+## CLI
+
+```
+$ is-docker
+```
+
+Exits with code 0 if inside a Docker container and 2 if not.