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/Services/Interfaces/IWorkerClient.cs

@@ -158,6 +158,10 @@ public interface IWorkerClient : INotifyPropertyChanged
     /// running. The exit code only exists in this process; the worker decides whether it was a
     /// list-handler session killed by the usage limit and reopens the same phase after the 5h reset.</summary>
     Task ReportInteractiveSessionExitedAsync(string taskId, int exitCode, CancellationToken ct = default);
+    /// <summary>The handler round's still-open (Queued/Running) tasks, for the Mission Control
+    /// "abandon run" action. Empty when the round has no entry or nothing open -- the caller then
+    /// closes the pane without a confirmation dialog.</summary>
+    Task<IReadOnlyList<HandlerOpenTaskDto>> GetHandlerOpenTasksAsync(string handlerTaskId, CancellationToken ct = default);
     /// <summary>Starts a planning session and returns the launch spec for an embedded ConPTY
     /// planning terminal (replaces StartPlanningSessionAsync's external wt window).</summary>
     Task<LaunchSpec> GetPlanningStartLaunchSpecAsync(string taskId, CancellationToken ct = default);