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/IMissionControlPane.cs

@@ -1,10 +1,9 @@
 namespace ClaudeDo.Ui.ViewModels.MissionControl;
 
 /// <summary>
-/// Common contract for anything hosted as a pane in the Command Center — implemented by both
-/// the streamed-log <see cref="ClaudeDo.Ui.ViewModels.Islands.TaskMonitorViewModel"/> and the
-/// embedded ConPTY <see cref="ConPtyPaneViewModel"/> — so the layout toggle (grid/tabs) can
-/// bind one heterogeneous pane collection.
+/// Common contract for anything hosted as a pane in the Command Center — currently only
+/// <see cref="ConPtyPaneViewModel"/>, kept as its own abstraction so the grid/tabs layout
+/// toggle binds a pane collection rather than a concrete ConPTY-specific type.
 /// </summary>
 public interface IMissionControlPane
 {