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/ViewModels/IslandsShellViewModel.cs

@@ -213,7 +213,6 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
         Lists = lists; Tasks = tasks; Details = details; Worker = worker;
         MissionControl = missionControl;
         MissionControl.OpenInApp = id => _ = RevealTaskAsync(id);
-        MissionControl.ShowDetached = (monitor, reDock) => Dialogs?.ShowDetachedMonitor(monitor, reDock);
         MissionControl.OpenSettingsRequested = () => Lists.OpenSettingsCommand.Execute(null);
         MissionControl.ErrorReported += FlashFooterError;
         // Keep the task rows' "Interactive" chip in step with Mission Control's open ConPTY panes.