feat(ui): spinners for ConPTY session start and task refine

Both actions previously gave no feedback: opening a ConPTY session only created
the tile after the launch-spec roundtrip (which may build a worktree), and the
refine button just disappeared while the run was in flight.

Add a shared Ellipse.spinner style, and let ConPtyPaneViewModel resolve its own
launch spec so the tile shows up immediately with a starting overlay. A failed
launch now keeps the tile with its inline error banner instead of never
appearing — Start() is separated from the ctor so the host can subscribe to
ErrorReported before the launch begins.

src/ClaudeDo.Ui/ViewModels/MissionControl/ConPtyPaneViewModel.cs

@@ -35,18 +35,44 @@ public sealed partial class ConPtyPaneViewModel : ViewModelBase, IMissionControl
     public event Action<string>? SubmitForReviewRequested;
 
     /// <summary>Task-based pane — dedup'd by <see cref="TaskId"/>. Pass null for an ad-hoc pane
-    /// (no task, never deduped); prefer <see cref="CreateAdHoc"/> at ad-hoc call sites.</summary>
-    public ConPtyPaneViewModel(string? taskId, string displayTitle, TerminalLaunchDescriptor descriptor)
+    /// (no task, never deduped); prefer <see cref="CreateAdHoc"/> at ad-hoc call sites.
+    /// <paramref name="descriptorFactory"/> is resolved by the pane itself (in <see cref="Start"/>)
+    /// so the tile — and its starting spinner — is visible while the launch spec is still being
+    /// fetched. The host must wire its handlers and then call <see cref="Start"/>.</summary>
+    public ConPtyPaneViewModel(
+        string? taskId,
+        string displayTitle,
+        Func<System.Threading.Tasks.Task<TerminalLaunchDescriptor>> descriptorFactory)
     {
         TaskId = taskId;
         _displayTitle = displayTitle;
+        _descriptorFactory = descriptorFactory;
         Terminal.PropertyChanged += OnTerminalPropertyChanged;
-        Terminal.Start(descriptor);
+    }
+
+    private readonly Func<System.Threading.Tasks.Task<TerminalLaunchDescriptor>> _descriptorFactory;
+
+    /// <summary>Resolves the launch spec and spawns the session. Call after wiring
+    /// <see cref="ErrorReported"/> so a failed launch is not swallowed.</summary>
+    public void Start() => _ = StartAsync();
+
+    private async System.Threading.Tasks.Task StartAsync()
+    {
+        try
+        {
+            Terminal.Start(await _descriptorFactory());
+        }
+        catch (Exception ex)
+        {
+            Terminal.ReportStartFailure(ex.Message);
+        }
     }
 
     /// <summary>Ad-hoc pane — no task, no dedup.</summary>
-    public static ConPtyPaneViewModel CreateAdHoc(string displayTitle, TerminalLaunchDescriptor descriptor)
-        => new(null, displayTitle, descriptor);
+    public static ConPtyPaneViewModel CreateAdHoc(
+        string displayTitle,
+        Func<System.Threading.Tasks.Task<TerminalLaunchDescriptor>> descriptorFactory)
+        => new(null, displayTitle, descriptorFactory);
 
     private void OnTerminalPropertyChanged(object? sender, PropertyChangedEventArgs e)
     {