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/calcSeverityCounts.js

@@ -0,0 +1,21 @@
+'use strict';
+
+/**
+ * @typedef {import('stylelint').Severity} Severity
+ *
+ * @param {Severity} severity
+ * @param {Record<Severity, number>} counts
+ * @returns {void}
+ */
+module.exports = function calcSeverityCounts(severity, counts) {
+	switch (severity) {
+		case 'error':
+			counts.error += 1;
+			break;
+		case 'warning':
+			counts.warning += 1;
+			break;
+		default:
+			throw new Error(`Unknown severity: "${severity}"`);
+	}
+};