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/Services/IDialogService.cs

@@ -1,8 +1,6 @@
-using System;
 using System.Threading.Tasks;
 using ClaudeDo.Ui.ViewModels;
 using ClaudeDo.Ui.ViewModels.Conflicts;
-using ClaudeDo.Ui.ViewModels.Islands;
 using ClaudeDo.Ui.ViewModels.Modals;
 
 namespace ClaudeDo.Ui.Services;
@@ -37,7 +35,4 @@ public interface IDialogService
 
     /// <summary>Show (or re-show + focus) the modeless Mission Control window. Lazily created; hides on close.</summary>
     void ShowMissionControl(MissionControlViewModel vm);
-
-    /// <summary>Show a detached monitor in its own window; <paramref name="onClosed"/> re-docks it when that window closes.</summary>
-    void ShowDetachedMonitor(TaskMonitorViewModel monitor, Action onClosed);
 }