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/formatters/jsonFormatter.js

@@ -0,0 +1,20 @@
+'use strict';
+
+/**
+ * Omit any properties starting with `_`, which are fake-private
+ *
+ * @type {import('stylelint').Formatter}
+ */
+module.exports = function jsonFormatter(results) {
+	const cleanedResults = results.map((result) =>
+		Object.entries(result)
+			.filter(([key]) => !key.startsWith('_'))
+			.reduce((/** @type {{ [key: string]: any }} */ obj, [key, value]) => {
+				obj[key] = value;
+
+				return obj;
+			}, {}),
+	);
+
+	return JSON.stringify(cleanedResults);
+};