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/unique-string/readme.md

@@ -0,0 +1,32 @@
+# unique-string [![Build Status](https://travis-ci.org/sindresorhus/unique-string.svg?branch=master)](https://travis-ci.org/sindresorhus/unique-string)
+
+> Generate a unique random string
+
+
+## Install
+
+```
+$ npm install unique-string
+```
+
+
+## Usage
+
+```js
+const uniqueString = require('unique-string');
+
+uniqueString();
+//=> 'b4de2a49c8ffa3fbee04446f045483b2'
+```
+
+
+## API
+
+### uniqueString()
+
+Returns a 32 character unique string. Matches the length of MD5, which is [unique enough](https://stackoverflow.com/a/2444336/64949) for non-crypto purposes.
+
+
+## License
+
+MIT © [Sindre Sorhus](https://sindresorhus.com)