feat(claude-do): merge UI-Prozess loggt auf Platte (ui-.log) + fehlgeschlagene Hub-

ClaudeDo-Task: d2ae3831-733f-4d40-93d7-70c93da11590

src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs

@@ -208,6 +208,9 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
 
     private void FlashFooter(string message, WorkerLogLevel level)
     {
+        if (level == WorkerLogLevel.Error)
+            Serilog.Log.Warning("Footer error: {message}", message);
+
         WorkerLogText = $"{DateTime.Now:HH:mm} · {message}";
         WorkerLogLevel = level;
         IsWorkerLogVisible = true;