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/postcss-resolve-nested-selector/README.md

@@ -0,0 +1,65 @@
+# postcss-resolve-nested-selector
+
+[![test](https://github.com/csstools/postcss-resolve-nested-selector/actions/workflows/test.yml/badge.svg?branch=main)](https://github.com/csstools/postcss-resolve-nested-selector/actions/workflows/test.yml)
+
+Given a (nested) selector in a PostCSS AST, return an array of resolved selectors.
+
+Tested to work with the syntax of [postcss-nested](https://github.com/postcss/postcss-nested).
+Should also work with SCSS and Less syntax. If you'd like to help out by
+adding some automated tests for those, that'd be swell. In fact, if you'd
+like to add any automated tests, you are a winner!
+
+If you want to resolve selectors in the same style as [postcss-nesting](https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-nesting) you should instead use [selector-resolve-nested](https://github.com/csstools/postcss-plugins/tree/main/packages/selector-resolve-nested)
+
+## API
+
+`resolveNestedSelector(selector, node)`
+
+Returns an array of selectors resolved from `selector`.
+
+For example, given this JS:
+
+```js
+var resolvedNestedSelector = require('postcss-resolve-nested-selector');
+postcssRoot.eachRule(function(rule) {
+	rule.selectors.forEach(function(selector) {
+		console.log(resolvedNestedSelector(selector, rule));
+	});
+});
+```
+
+And the following CSS:
+
+```scss
+.foo {
+	.bar {
+		color: pink;
+	}
+}
+```
+
+This should log:
+
+```
+['.foo']
+['.foo .bar']
+```
+
+Or with this CSS:
+
+```scss
+.foo {
+	.bar &,
+	a {
+		color: pink;
+	}
+}
+```
+
+This should log:
+
+```
+['.foo']
+['.bar .foo']
+['.foo a']
+```