fix(ui): mark transaction document links as external

Add external prop to UButton components linking to document URLs
Prevents the router from intercepting external downloads

app/pages/confirmation/[token].vue

@@ -500,6 +500,7 @@ async function cancelBookingConfirmation() {
               <div class="flex flex-col gap-2 sm:flex-row sm:items-center">
                 <UButton
                   :to="booking.transactionDocument.url"
+                  external
                   :label="t('confirm.download')"
                   color="neutral"
                   variant="outline"