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/read-pkg-up/readme.md

@@ -0,0 +1,77 @@
+# read-pkg-up [![Build Status](https://travis-ci.org/sindresorhus/read-pkg-up.svg?branch=master)](https://travis-ci.org/sindresorhus/read-pkg-up)
+
+> Read the closest package.json file
+
+## Why
+
+- [Finds the closest package.json](https://github.com/sindresorhus/find-up)
+- [Gracefully handles filesystem issues](https://github.com/isaacs/node-graceful-fs)
+- [Throws more helpful JSON errors](https://github.com/sindresorhus/parse-json)
+- [Normalizes the data](https://github.com/npm/normalize-package-data#what-normalization-currently-entails)
+
+## Install
+
+```
+$ npm install read-pkg-up
+```
+
+## Usage
+
+```js
+const readPkgUp = require('read-pkg-up');
+
+(async () => {
+	console.log(await readPkgUp());
+	/*
+	{
+		packageJson: {
+			name: 'awesome-package',
+			version: '1.0.0',
+			…
+		},
+		path: '/Users/sindresorhus/dev/awesome-package/package.json'
+	}
+	*/
+})();
+```
+
+## API
+
+### readPkgUp(options?)
+
+Returns a `Promise<object>` or `Promise<undefined>` if no `package.json` was found.
+
+### readPkgUp.sync(options?)
+
+Returns the result object or `undefined` if no `package.json` was found.
+
+#### options
+
+Type: `object`
+
+##### cwd
+
+Type: `string`\
+Default: `process.cwd()`
+
+Directory to start looking for a package.json file.
+
+##### normalize
+
+Type: `boolean`\
+Default: `true`
+
+[Normalize](https://github.com/npm/normalize-package-data#what-normalization-currently-entails) the package data.
+
+## read-pkg-up for enterprise
+
+Available as part of the Tidelift Subscription.
+
+The maintainers of read-pkg-up and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/npm-read-pkg-up?utm_source=npm-read-pkg-up&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)
+
+## Related
+
+- [read-pkg](https://github.com/sindresorhus/read-pkg) - Read a package.json file
+- [pkg-up](https://github.com/sindresorhus/pkg-up) - Find the closest package.json file
+- [find-up](https://github.com/sindresorhus/find-up) - Find a file by walking up parent directories
+- [pkg-conf](https://github.com/sindresorhus/pkg-conf) - Get namespaced config from the closest package.json