feat: improved promotional and purchase vouchers

src/Validator/Constraints/PurchaseVoucher.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Validates purchase voucher codes via BPN API.
+ *
+ * Checks that the voucher exists and has remaining balance.
+ * Applied at ParticipantEditDto level to access booking context.
+ */
+#[\Attribute]
+class PurchaseVoucher extends Constraint
+{
+    public string $message = 'Gutschein ungültig: {{ error }}';
+
+    public function getTargets(): array|string
+    {
+        return static::CLASS_CONSTRAINT;
+    }
+}