feat(interactive): host task-based ConPTY sessions in Command Center

Adds an 'Open ConPTY session' entry that fetches a task's launch spec and hosts
an embedded ConPTY terminal as a Mission Control pane, coexisting with the
streamed-log monitor panes (streaming stack untouched). Introduces IMissionControlPane
+ ConPtyPaneViewModel, a non-destructive Panes mirror (Monitors prefix + ConPtySessions
suffix) so unrelated monitor churn never tears down a live terminal, and a grid<->tabs
layout toggle. Launch failures surface via the footer error strip.

src/ClaudeDo.Ui/ViewModels/MissionControl/IMissionControlPane.cs

@@ -0,0 +1,12 @@
+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.
+/// </summary>
+public interface IMissionControlPane
+{
+    string DisplayTitle { get; }
+}