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/querystringify/README.md

@@ -0,0 +1,61 @@
+# querystringify
+
+[![Version npm](http://img.shields.io/npm/v/querystringify.svg?style=flat-square)](https://www.npmjs.com/package/querystringify)[![Build Status](http://img.shields.io/travis/unshiftio/querystringify/master.svg?style=flat-square)](https://travis-ci.org/unshiftio/querystringify)[![Dependencies](https://img.shields.io/david/unshiftio/querystringify.svg?style=flat-square)](https://david-dm.org/unshiftio/querystringify)[![Coverage Status](http://img.shields.io/coveralls/unshiftio/querystringify/master.svg?style=flat-square)](https://coveralls.io/r/unshiftio/querystringify?branch=master)
+
+A somewhat JSON compatible interface for query string parsing. This query string
+parser is dumb, don't expect to much from it as it only wants to parse simple
+query strings. If you want to parse complex, multi level and deeply nested
+query strings then you should ask your self. WTF am I doing?
+
+## Installation
+
+This module is released in npm as `querystringify`. It's also compatible with
+`browserify` so it can be used on the server as well as on the client. To
+install it simply run the following command from your CLI:
+
+```
+npm install --save querystringify
+```
+
+## Usage
+
+In the following examples we assume that you've already required the library as:
+
+```js
+'use strict';
+
+var qs = require('querystringify');
+```
+
+### qs.parse()
+
+The parse method transforms a given query string in to an object. Parameters
+without values are set to empty strings. It does not care if your query string
+is prefixed with a `?`, a `#`, or not prefixed. It just extracts the parts
+between the `=` and `&`:
+
+```js
+qs.parse('?foo=bar');         // { foo: 'bar' }
+qs.parse('#foo=bar');         // { foo: 'bar' }
+qs.parse('foo=bar');          // { foo: 'bar' }
+qs.parse('foo=bar&bar=foo');  // { foo: 'bar', bar: 'foo' }
+qs.parse('foo&bar=foo');      // { foo: '', bar: 'foo' }
+```
+
+### qs.stringify()
+
+This transforms a given object in to a query string. By default we return the
+query string without a `?` prefix. If you want to prefix it by default simply
+supply `true` as second argument. If it should be prefixed by something else
+simply supply a string with the prefix value as second argument:
+
+```js
+qs.stringify({ foo: bar });       // foo=bar
+qs.stringify({ foo: bar }, true); // ?foo=bar
+qs.stringify({ foo: bar }, '#');  // #foo=bar
+qs.stringify({ foo: '' }, '&');   // &foo=
+```
+
+## License
+
+MIT