feat: voucher purchase flow

src/BusProNet/Model/VoucherPreview.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\BusProNet\Model;
+
+/**
+ * The GUTSCHEINVORSCHAU response, decoded from its data URI to the raw PDF bytes.
+ */
+final readonly class VoucherPreview
+{
+    public function __construct(
+        public string $pdf,
+    ) {
+    }
+}