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/isAfterSingleLineComment.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const isSharedLineComment = require('./isSharedLineComment');
+
+/**
+ * @param {import('postcss').Node} node
+ */
+function isAfterSingleLineComment(node) {
+	const prevNode = node.prev();
+
+	return (
+		prevNode !== undefined &&
+		prevNode.type === 'comment' &&
+		!isSharedLineComment(prevNode) &&
+		prevNode.source &&
+		prevNode.source.start &&
+		prevNode.source.end &&
+		prevNode.source.start.line === prevNode.source.end.line
+	);
+}
+
+module.exports = isAfterSingleLineComment;