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>".

tests/ClaudeDo.Worker.Tests/UiVm/TaskRowViewModelTests.cs

@@ -22,6 +22,24 @@ public class TaskRowViewModelTests
         Assert.Equal(expected, vm.StatusChipClass);
     }
 
+    [Fact]
+    public void Number_SetFromEntity_SurvivesUpdateFromEntity()
+    {
+        var entity = new TaskEntity
+        {
+            Id = "t", ListId = "l1", Title = "Task", Number = 123, CreatedAt = DateTime.UtcNow,
+        };
+        var vm = TaskRowViewModel.FromEntity(entity);
+        Assert.Equal(123, vm.Number);
+
+        // Simulates the TaskUpdated refresh path: the entity is re-fetched and the same
+        // row is updated in place rather than replaced.
+        entity.Title = "Task (edited)";
+        vm.UpdateFromEntity(entity);
+
+        Assert.Equal(123, vm.Number);
+    }
+
     [Fact]
     public void IsDropTarget_Follows_Either_DropHint_And_Raises_PropertyChanged()
     {