fix(notification-outbox): fall back to Target for empty notification list name

src/ScadaLink.StoreAndForward/NotificationForwarder.cs

@@ -115,7 +115,10 @@ public sealed class NotificationForwarder
 
         submit = new NotificationSubmit(
             NotificationId: message.Id,
-            ListName: payload.ListName ?? message.Target,
+            // A null OR empty/blank ListName falls back to the S&F Target — matching the
+            // empty-string guard the former SMTP handler (NotificationDeliveryService)
+            // applied, so an empty list name is never forwarded to central.
+            ListName: string.IsNullOrEmpty(payload.ListName) ? message.Target : payload.ListName,
             Subject: payload.Subject ?? string.Empty,
             Body: payload.Message ?? string.Empty,
             SourceSiteId: _sourceSiteId,