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/object.values/implementation.js

@@ -0,0 +1,17 @@
+'use strict';
+
+var RequireObjectCoercible = require('es-object-atoms/RequireObjectCoercible');
+var callBound = require('call-bound');
+
+var $isEnumerable = callBound('Object.prototype.propertyIsEnumerable');
+
+module.exports = function values(O) {
+	var obj = RequireObjectCoercible(O);
+	var vals = [];
+	for (var key in obj) {
+		if ($isEnumerable(obj, key)) { // checks own-ness as well
+			vals[vals.length] = obj[key];
+		}
+	}
+	return vals;
+};