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/escape-string-regexp/readme.md

@@ -0,0 +1,34 @@
+# escape-string-regexp [![Build Status](https://travis-ci.org/sindresorhus/escape-string-regexp.svg?branch=master)](https://travis-ci.org/sindresorhus/escape-string-regexp)
+
+> Escape RegExp special characters
+
+## Install
+
+```
+$ npm install escape-string-regexp
+```
+
+## Usage
+
+```js
+const escapeStringRegexp = require('escape-string-regexp');
+
+const escapedString = escapeStringRegexp('How much $ for a 🦄?');
+//=> 'How much \\$ for a 🦄\\?'
+
+new RegExp(escapedString);
+```
+
+You can also use this to escape a string that is inserted into the middle of a regex, for example, into a character class.
+
+---
+
+<div align="center">
+	<b>
+		<a href="https://tidelift.com/subscription/pkg/npm-escape-string-regexp?utm_source=npm-escape-string-regexp&utm_medium=referral&utm_campaign=readme">Get professional support for this package with a Tidelift subscription</a>
+	</b>
+	<br>
+	<sub>
+		Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies.
+	</sub>
+</div>