fix(thank-you): serve GiroCode as signed PNG URL instead of data URL

app/services/invoice/girocode.ts

@@ -61,3 +61,15 @@ export async function buildGiroCodeDataUrl(
     width: 256,
   });
 }
+
+export async function buildGiroCodePngBuffer(
+  input: GiroCodeInput,
+): Promise<Buffer> {
+  const payload = buildGiroCodePayload(input);
+  return QRCode.toBuffer(payload, {
+    errorCorrectionLevel: "M",
+    margin: 1,
+    width: 256,
+    type: "png",
+  });
+}