feat(ui,worker): surface task numbers in row/detail UI and worker log

Slice 4/5 of task-numbers: TaskRowViewModel.Number renders as a dimmed
"#123" before the row title; DetailsIslandViewModel.TaskIdBadge now
shows "#123" instead of the unusable "#T<guid-prefix>" handle; and the
curated WorkerLog business events in TaskRunner, TaskMergeService, and
TaskResetService prefix their quoted title with "#<Number>".

src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs

@@ -190,7 +190,7 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
 
     public string SessionLabel => "claude-session";
 
-    public string TaskIdBadge => Task != null ? $"#T{Task.Id[..Math.Min(3, Task.Id.Length)].ToUpperInvariant()}" : "";
+    public string TaskIdBadge => Task != null ? $"#{Task.Number}" : "";
 
     [ObservableProperty]
     [NotifyCanExecuteChangedFor(nameof(ContinueCommand))]