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/lighthouse-stack-packs/README.md

@@ -0,0 +1,28 @@
+# Lighthouse Stack Packs
+
+[Lighthouse](https://github.com/GoogleChrome/lighthouse) provides developers with guidance to improve their site by auditing for performance, accessibility and other best practices.
+
+Many developers today use different technologies (backend/CMS/JavaScript frameworks) to build their web pages. Instead of only surfacing general recommendations, what if Lighthouse could also provide more relevant and actionable advice depending on the tools used?
+
+**Stack Packs** allow Lighthouse to detect what platform your site is built on and display specific stack-based recommendations. These recommendations are defined and curated by experts from the community.
+
+<p align="center">
+  <img alt="Prototype" title="Prototype" src="https://raw.githubusercontent.com/GoogleChrome/lighthouse-stack-packs/master/image-example.png">
+</p>
+
+## Supported
+
+* AMP
+* Angular
+* Drupal
+* Gatsby
+* Magento
+* Next.js
+* Nuxt
+* React
+* WordPress
+* WP Rocket
+
+## Contributing
+
+Interested in contributing? Please read the [contributing guidelines](./CONTRIBUTING.md)!