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.

tests/ClaudeDo.Ui.Tests/ViewModels/TasksIslandMoveToListTests.cs

@@ -68,7 +68,6 @@ public class TasksIslandMoveToListTests : IDisposable
         public Task ShowLogVisualizerAsync(LogVisualizerViewModel vm) => throw new NotImplementedException();
         public Task ShowErrorAsync(string message) => Task.CompletedTask;
         public void ShowMissionControl(MissionControlViewModel vm) => throw new NotImplementedException();
-        public void ShowDetachedMonitor(TaskMonitorViewModel monitor, Action onClosed) => throw new NotImplementedException();
     }
 
     private TasksIslandViewModel BuildViewModel() => new(new TestDbFactory(NewContext), worker: null);