feat(ui): Mission-Control-Kacheln behalten Position und Identitaetsfarbe ueber Handoffs

Ein Handoff schloss die alte Pane und haengte die neue hinten an -- die Kachel
sprang ans Ende und das ganze Grid ordnete sich neu. Die neue Pane wird jetzt am
Index der alten eingesetzt.

Dazu bekommt jede Kachel eine aus IdentityKey (Default: TaskId) abgeleitete Farbe:
3px-Streifen links am Tile, Punkt im Focus-Mode-Tab. Kein State, keine Persistenz --
derselbe Task faerbt nach App-Neustart gleich, und ein Handoff erbt die Farbe, weil
er dieselbe TaskId behaelt. Nur kuehle Hues, damit nichts als Status gelesen wird.

src/ClaudeDo.Ui/ViewModels/MissionControlViewModel.cs

@@ -408,6 +408,11 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
         if (string.IsNullOrEmpty(taskId) || survivingTaskIds is not { Count: > 0 }) return;
         OpenRequested?.Invoke();
 
+        // Keep the tile where it was: the incoming phase re-enters at the outgoing pane's slot
+        // instead of being appended, so a handoff doesn't reshuffle every other tile in the grid.
+        var slot = ConPtySessions.FirstOrDefault(s => s.TaskId == taskId) is { } first
+            ? ConPtySessions.IndexOf(first)
+            : (int?)null;
         foreach (var stale in ConPtySessions.Where(s => s.TaskId == taskId).ToList())
             CloseConPtySession(stale);
 
@@ -428,7 +433,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
 
         AddConPtyPane(new ConPtyPaneViewModel(taskId, title,
             () => DescribeAsync(() => _worker.GetMergeHelperHandoffLaunchSpecAsync(taskId, survivingTaskIds, nextPhase)))
-            { IsListHandler = true });
+            { IsListHandler = true }, slot);
     }
 
     // The 5h usage window is about to run out under this handler session: type the worker's warning
@@ -446,14 +451,14 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
 
     // Wires a freshly built pane and shows it immediately — the pane resolves its own launch spec,
     // so the tile is on screen (spinner running) while the worker is still preparing the worktree.
-    private void AddConPtyPane(ConPtyPaneViewModel pane)
+    private void AddConPtyPane(ConPtyPaneViewModel pane, int? index = null)
     {
         pane.ErrorReported += OnConPtyPaneError;
         pane.CloseRequested += OnPaneCloseRequested;
         pane.SubmitForReviewRequested += OnPaneSubmitForReview;
         pane.SessionDiedAfterStartup += OnPaneSessionDied;
         pane.AbandonRunRequested += OnPaneAbandonRun;
-        ConPtySessions.Add(pane);
+        ConPtySessions.Insert(Math.Min(index ?? ConPtySessions.Count, ConPtySessions.Count), pane);
         pane.Start();
     }