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/mixin-object/README.md

@@ -0,0 +1,75 @@
+# mixin-object [![NPM version](https://badge.fury.io/js/mixin-object.svg)](http://badge.fury.io/js/mixin-object)
+
+> Mixin the own and inherited properties of other objects onto the first object. Pass an empty object as the first arg to shallow clone.
+
+If you only want to combine own-properties, use [extend-shallow](https://github.com/jonschlinkert/extend-shallow).
+
+## Install
+
+Install with [npm](https://www.npmjs.com/)
+
+```sh
+$ npm i mixin-object --save
+```
+
+Install with [bower](http://bower.io/)
+
+```sh
+$ bower install mixin-object --save
+```
+
+## Usage
+
+```js
+var mixin = require('mixin-object');
+
+var obj = {c: 'c'};
+var foo = mixin({a: 'a'}, {b: 'b'});
+console.log(foo);
+//=> {c: 'c', a: 'a', b: 'b'}
+console.log(obj);
+//=> {c: 'c'}
+
+mixin({}, {a: 'a'}, {b: 'b'});
+//=> {a: 'a', b: 'b'}
+```
+
+## Related
+
+* [assign-deep](https://github.com/jonschlinkert/assign-deep): Deeply assign the enumerable properties of source objects to a destination object.
+* [defaults-deep](https://github.com/jonschlinkert/defaults-deep): Like `extend` but recursively copies only the missing properties/values to the target object.
+* [extend-shallow](https://github.com/jonschlinkert/extend-shallow): Extend an object with the properties of additional objects. node.js/javascript util.
+* [for-own](https://github.com/jonschlinkert/for-own): Iterate over the own enumerable properties of an object, and return an object with properties… [more](https://github.com/jonschlinkert/for-own)
+* [for-in](https://github.com/jonschlinkert/for-in): Iterate over the own and inherited enumerable properties of an objecte, and return an object… [more](https://github.com/jonschlinkert/for-in)
+* [isobject](https://github.com/jonschlinkert/isobject): Returns true if the value is an object and not an array or null.
+* [is-plain-object](https://github.com/jonschlinkert/is-plain-object): Returns true if an object was created by the `Object` constructor.
+* [mixin-deep](https://github.com/jonschlinkert/mixin-deep): Deeply mix the properties of objects into the first object. Like merge-deep, but doesn't clone.
+* [merge-deep](https://github.com/jonschlinkert/merge-deep): Recursively merge values in a javascript object.
+
+## Running tests
+
+Install dev dependencies:
+
+```sh
+$ npm i -d && npm test
+```
+
+## Contributing
+
+Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](https://github.com/jonschlinkert/mixin-object/issues/new)
+
+## Author
+
+**Jon Schlinkert**
+
++ [github/jonschlinkert](https://github.com/jonschlinkert)
++ [twitter/jonschlinkert](http://twitter.com/jonschlinkert)
+
+## License
+
+Copyright © 2014-2015 [Jon Schlinkert](https://github.com/jonschlinkert)
+Released under the MIT license.
+
+***
+
+_This file was generated by [verb-cli](https://github.com/assemble/verb-cli) on July 05, 2015._