chore(ui): remove dead Mission Control monitor-pane stack

Auto-seeding of monitor tiles was disabled in 724814f; Mission Control now
only shows ConPTY panes. Removes Monitors/EnsureMonitor/SeedActive, the
detach/re-dock machinery, MonitorPaneView and the detached monitor window,
plus their tests and orphaned localization keys.

TaskMonitorViewModel itself stays: DetailsIslandViewModel still uses it as
the backing state for the task Log/AgentState/AskUser-question UI, so only
its Mission-Control-only members (Title/DisplayTitle, detach, cancel command,
IMissionControlPane) were stripped. IMissionControlPane/Panes were kept
(now a 1:1 mirror of ConPtySessions) rather than dissolved, to avoid
churning the still-live ConPTY pane tests and AXAML for a single-implementer
interface.

Visual verification still open: Mission Control with several open ConPTY
tiles, and the Focus/Overview toggle.

src/ClaudeDo.Ui/Views/WindowDialogService.cs

@@ -9,7 +9,6 @@ using Avalonia.Media;
 using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels;
 using ClaudeDo.Ui.ViewModels.Conflicts;
-using ClaudeDo.Ui.ViewModels.Islands;
 using ClaudeDo.Ui.ViewModels.Modals;
 using ClaudeDo.Ui.Views.Conflicts;
 using ClaudeDo.Ui.Views.MissionControl;
@@ -146,13 +145,6 @@ public sealed class WindowDialogService : IDialogService
         _missionControl.Activate();          // bring to front / focus
     }
 
-    public void ShowDetachedMonitor(TaskMonitorViewModel monitor, Action onClosed)
-    {
-        var win = new TaskMonitorWindow { DataContext = monitor };
-        win.Closed += (_, _) => onClosed();   // closing re-docks into the grid
-        win.Show();                            // modeless, independent
-    }
-
     public Task<bool> ConfirmAsync(string message)
     {
         var tcs = new TaskCompletionSource<bool>();