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/arrayEqual.js

@@ -0,0 +1,16 @@
+'use strict';
+
+/**
+ * Tests if two arrays are equal.
+ *
+ * @param {unknown} a
+ * @param {unknown} b
+ * @returns {boolean}
+ */
+module.exports = function arrayEqual(a, b) {
+	if (!Array.isArray(a) || !Array.isArray(b)) return false;
+
+	if (a.length !== b.length) return false;
+
+	return a.every((elem, index) => elem === b[index]);
+};