DeliveryNote: Set date to be mtime

Elwig/Documents/DeliveryNote.cs

@@ -32,6 +32,7 @@ namespace Elwig.Documents {
             Delivery = d;
             Text = App.Client.TextDeliveryNote;
             DocumentId = d.LsNr;
+            Date = DateOnly.FromDateTime(d.ModifiedAt);
             IsDoublePaged = true;
             MemberBuckets = ctx?.GetMemberBuckets(d.Year, d.Member.MgNr).GetAwaiter().GetResult() ?? [];
         }