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/MissionControl/ConPtyPaneViewModel.cs

@@ -9,9 +9,7 @@ namespace ClaudeDo.Ui.ViewModels.MissionControl;
 /// <summary>
 /// Command Center pane hosting an embedded ConPTY terminal for either one task's interactive
 /// Claude session, or an ad-hoc/free session in a user-chosen directory (no task, <see cref="TaskId"/>
-/// is null — ad-hoc panes are never deduped, unlike task-based ones). Distinct from the streamed-log
-/// <see cref="ClaudeDo.Ui.ViewModels.Islands.TaskMonitorViewModel"/> pane; the two coexist until
-/// the streaming interactive stack is removed.
+/// is null — ad-hoc panes are never deduped, unlike task-based ones).
 /// </summary>
 public sealed partial class ConPtyPaneViewModel : ViewModelBase, IMissionControlPane, IDisposable
 {