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/stylelint/lib/utils/isContextFunctionalPseudoClass.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const {
+	aNPlusBOfSNotationPseudoClasses,
+	logicalCombinationsPseudoClasses,
+} = require('../reference/selectors');
+
+/**
+ * Check whether a node is a context-functional pseudo-class (i.e. either a logical combination
+ * or a 'aNPlusBOfSNotationPseudoClasses' / tree-structural pseudo-class)
+ *
+ * @param {import('postcss-selector-parser').Node} node - postcss-selector-parser node (of type pseudo)
+ * @return {node is import('postcss-selector-parser').Pseudo} If `true`, the node is a context-functional pseudo-class
+ */
+module.exports = function isContextFunctionalPseudoClass(node) {
+	if (node.type === 'pseudo') {
+		const normalisedParentName = node.value.toLowerCase().replace(/:+/, '');
+
+		return (
+			logicalCombinationsPseudoClasses.has(normalisedParentName) ||
+			aNPlusBOfSNotationPseudoClasses.has(normalisedParentName)
+		);
+	}
+
+	return false;
+};