chore(claude-do): Task-row visual fixes: chain step badge z-order + hide "#0"

From the 2026-08-11 unpushed-commit review (Low). Both in `src/ClaudeDo.Ui/Views/Islands/TaskRowView.axaml`. **Visual verification by the user is required — do not claim either is fixed without a screenshot; list both as open visual checks in the result.**

## A) Chain step badge is drawn under the task card

Commit `eb66ae7` moved `Border.chain-step-badge` from column 0 into column 1 with `Margin

ClaudeDo-Task: 9ec7d4ea-272b-4645-8da4-41ff3621f2f0

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

@@ -73,6 +73,10 @@ public sealed partial class TaskRowViewModel : ViewModelBase
     public int StepsCount { get; init; }
     public int StepsCompleted { get; init; }
 
+    // Number is 0 for rows created outside TaskNumberAllocator (test seeds, a future import
+    // path); a bare "#0" would be meaningless, so hide the badge entirely below 1.
+    public bool ShowNumberBadge   => Number > 0;
+
     public bool IsChild            => !string.IsNullOrEmpty(ParentTaskId);
     public bool IsAgentSuggested   => IsChild && !string.IsNullOrEmpty(CreatedBy) && CreatedBy == ParentTaskId;
     public bool IsPlanningParent => PlanningPhase != PlanningPhase.None
@@ -318,6 +322,7 @@ public sealed partial class TaskRowViewModel : ViewModelBase
         OnPropertyChanged(nameof(CanQueuePlan));
     }
 
+    partial void OnNumberChanged(int value)        => OnPropertyChanged(nameof(ShowNumberBadge));
     partial void OnBranchChanged(string? value)    => OnPropertyChanged(nameof(HasBranch));
     partial void OnWorktreeStateChanged(ClaudeDo.Data.Models.WorktreeState? value)
     {