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/cssstyle/README.md

@@ -0,0 +1,15 @@
+# CSSStyleDeclaration
+
+A Node JS implementation of the CSS Object Model [CSSStyleDeclaration interface](https://www.w3.org/TR/cssom-1/#the-cssstyledeclaration-interface).
+
+[![NpmVersion](https://img.shields.io/npm/v/cssstyle.svg)](https://www.npmjs.com/package/cssstyle) [![Build Status](https://travis-ci.org/jsdom/cssstyle.svg?branch=master)](https://travis-ci.org/jsdom/cssstyle) [![codecov](https://codecov.io/gh/jsdom/cssstyle/branch/master/graph/badge.svg)](https://codecov.io/gh/jsdom/cssstyle)
+
+---
+
+#### Background
+
+This package is an extension of the CSSStyleDeclaration class in Nikita Vasilyev's [CSSOM](https://github.com/NV/CSSOM) with added support for CSS 2 & 3 properties. The primary use case is for testing browser code in a Node environment. 
+
+It was originally created by Chad Walker, it is now maintaind by Jon Sakas and other open source contributors.
+
+Bug reports and pull requests are welcome.