feat(ui): route detail-pane review actions through OperationStatus

Approve, Submit, Reject, and Park each get their own OperationStatus so the
button locks and shows an OperationIndicator for the duration of the call;
Approve additionally scopes a MergeProgressEvent subscription to its own
task id to sharpen the label from "merging" to "verifying" mid-flight.
MergeSectionViewModel's preview refresh gets the same treatment for display
only, since it has no command button to gate.

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

@@ -1,6 +1,7 @@
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using System.Collections.ObjectModel;
+using ClaudeDo.Ui.Localization;
 using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels.Modals;
 using Microsoft.Extensions.DependencyInjection;
@@ -27,6 +28,10 @@ public sealed partial class MergeSectionViewModel : ViewModelBase
     [ObservableProperty] private ObservableCollection<string> _mergeTargetBranches = new();
     [ObservableProperty] private string? _selectedMergeTarget;
 
+    // No CanExecute to gate here — RefreshMergePreviewAsync is triggered from the Bind path,
+    // not a [RelayCommand], so PreviewOp only drives the indicator, never locks a button.
+    public OperationStatus PreviewOp { get; } = new();
+
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(ShowMergePreviewMuted))]
     private string _mergePreviewText = "";
@@ -118,6 +123,7 @@ public sealed partial class MergeSectionViewModel : ViewModelBase
         }
         var capturedTaskId = TaskId;
         var capturedTarget = SelectedMergeTarget;
+        using var op = PreviewOp.Begin(Loc.T("ops.review.previewing"));
         var dto = await _worker.PreviewMergeAsync(capturedTaskId, capturedTarget ?? "");
         if (TaskId != capturedTaskId || SelectedMergeTarget != capturedTarget) return;
         var (text, clean, conflict) = MergePreviewPresenter.Describe(dto);