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/TaskRowViewModel.cs

@@ -8,6 +8,7 @@ namespace ClaudeDo.Ui.ViewModels.Islands;
 public sealed partial class TaskRowViewModel : ViewModelBase
 {
     public required string Id { get; init; }
+    [ObservableProperty] private int _number;
     [ObservableProperty] private string _title = "";
     [ObservableProperty] private string _listName = "";
     [ObservableProperty] private bool _done;
@@ -351,6 +352,7 @@ public sealed partial class TaskRowViewModel : ViewModelBase
     public void UpdateFromEntity(TaskEntity t)
     {
         var (add, del) = ParseDiffStat(t.Worktree?.DiffStat);
+        Number            = t.Number;
         Title             = t.Title;
         ListName          = t.List?.Name ?? "";
         Done              = t.Status == TaskStatus.Done;