feat(mission-control): Handler-Run per Knopf abbrechen

Ein "Abandon run"-Knopf an Handler-Panes fragt HandlerRoundState.Get(handlerTaskId)
nach den noch offenen (Queued/Running) Tasks des Laufs, bestaetigt mit Anzahl,
cancelt jeden ueber den bestehenden CancelTaskAsync-Pfad und schliesst danach die
Session -- ein Schritt statt Tile schliessen + Queue separat abbrechen. Ohne
offene Tasks (oder ohne Round-Eintrag) schliesst die Aktion direkt, ohne Dialog.
Nur an den beiden Handler-Panes sichtbar (IsListHandler), normale Task-/Ad-hoc-
Panes bleiben unveraendert.

src/ClaudeDo.Ui/Views/MissionControl/MissionControlView.axaml.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Linq;
+using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Layout;
 using Avalonia.Media;
@@ -55,6 +56,7 @@ public partial class MissionControlView : UserControl
             _vm.Panes.CollectionChanged -= OnPanesChanged;
             _vm.PropertyChanged -= OnViewModelPropertyChanged;
             _vm.BrowseForSessionRequested = null;
+            _vm.ConfirmAsync = null;
         }
 
         _vm = DataContext as MissionControlViewModel;
@@ -64,12 +66,59 @@ public partial class MissionControlView : UserControl
             _vm.Panes.CollectionChanged += OnPanesChanged;
             _vm.PropertyChanged += OnViewModelPropertyChanged;
             _vm.BrowseForSessionRequested = BrowseForSessionAsync;
+            _vm.ConfirmAsync = ShowConfirmAsync;
         }
 
         RebuildOverviewGrid();
         UpdateQueueColumn();
     }
 
+    // Abandon-run confirmation -- same TaskCompletionSource-backed plain Window as
+    // TasksIslandView.ShowConfirmAsync (no shared control for this shape yet).
+    private async Task<bool> ShowConfirmAsync(string message)
+    {
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        if (owner is null) return false;
+
+        var tcs = new TaskCompletionSource<bool>();
+        var cancel = new Button { Content = "Cancel", MinWidth = 90 };
+        var confirm = new Button { Content = "Confirm", MinWidth = 90, Classes = { "danger" } };
+
+        var dialog = new Window
+        {
+            Title = "Confirm",
+            Width = 380,
+            SizeToContent = SizeToContent.Height,
+            CanResize = false,
+            WindowStartupLocation = WindowStartupLocation.CenterOwner,
+            ShowInTaskbar = false,
+            Background = this.FindResource("SurfaceBrush") as IBrush,
+            Content = new StackPanel
+            {
+                Margin = new Thickness(20),
+                Spacing = 16,
+                Children =
+                {
+                    new TextBlock { Text = message, TextWrapping = TextWrapping.Wrap },
+                    new StackPanel
+                    {
+                        Orientation = Orientation.Horizontal,
+                        HorizontalAlignment = HorizontalAlignment.Right,
+                        Spacing = 8,
+                        Children = { cancel, confirm },
+                    },
+                },
+            },
+        };
+
+        cancel.Click += (_, _) => { tcs.TrySetResult(false); dialog.Close(); };
+        confirm.Click += (_, _) => { tcs.TrySetResult(true); dialog.Close(); };
+        dialog.Closed += (_, _) => tcs.TrySetResult(false);
+
+        _ = dialog.ShowDialog(owner);
+        return await tcs.Task;
+    }
+
     private void OnPanesChanged(object? sender, NotifyCollectionChangedEventArgs e) => RebuildOverviewGrid();
 
     private void OnViewModelPropertyChanged(object? sender, PropertyChangedEventArgs e)