fix(claude-do): snake_case Serilog tokens + no Warning-log on cancelled hub calls

Message-template tokens must be snake_case (repo rule) -- fixes 4 PascalCase
tokens introduced in 57dd6766. TryInvokeAsync's swallowing catch also no
longer logs a Warning for OperationCanceledException, which is routine
(e.g. worker shutdown/reconnect), not a failure worth a trace.

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

src/ClaudeDo.Ui/ViewModels/IslandsShellViewModel.cs

@@ -209,7 +209,7 @@ 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);
+            Serilog.Log.Warning("Footer error: {message}", message);
 
         WorkerLogText = $"{DateTime.Now:HH:mm} · {message}";
         WorkerLogLevel = level;