feat(ui): triage model picker (opus/fable) in the merge helper start modal

src/ClaudeDo.Ui/ViewModels/Modals/MergeHelperSelectionModalViewModel.cs

@@ -67,6 +67,15 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
 
     public ObservableCollection<MergeHelperTaskRowViewModel> Tasks { get; } = new();
 
+    /// <summary>Model choices for the triage session. Only opus/fable are offered on purpose —
+    /// triage is the dedupe/refine leverage point; cheaper models aren't worth a picker slot.</summary>
+    public IReadOnlyList<string> ModelOptions { get; } = new[] { "opus", "fable" };
+
+    [ObservableProperty] private string _selectedModel = Data.Models.ModelRegistry.HandlerTriageAlias;
+
+    /// <summary>Hidden in review mode — those runs start directly at the merge phase, no triage.</summary>
+    public bool ShowModelPicker => !_reviewMode;
+
     [ObservableProperty] private string _scopeLabel = "";
 
     public bool HasTasks => Tasks.Count > 0;
@@ -100,6 +109,7 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
     {
         _reviewMode = true;
         ScopeLabel = Loc.T("modals.mergeHelper.scopeReview");
+        OnPropertyChanged(nameof(ShowModelPicker));
     }
 
     /// <summary>Groups a confirmed review-mode selection by owning list, preserving row order —