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/transformSelector.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const selectorParser = require('postcss-selector-parser');
+
+/**
+ * @param {import('stylelint').PostcssResult} result
+ * @param {import('postcss').Rule} node
+ * @param {(root: import('postcss-selector-parser').Root) => void} callback
+ * @returns {string | undefined}
+ */
+module.exports = function transformSelector(result, node, callback) {
+	try {
+		return selectorParser(callback).processSync(node, { updateSelector: true });
+	} catch {
+		result.warn('Cannot parse selector', { node, stylelintType: 'parseError' });
+
+		return undefined;
+	}
+};