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.

tests/ClaudeDo.Ui.Tests/ViewModels/TaskMonitorViewModelTests.cs

@@ -109,18 +109,6 @@ public class TaskMonitorViewModelTests : IDisposable
         Assert.True(vm.HasRoadblock);
     }
 
-    [Fact]
-    public void Detach_WhenNotDetached_InvokesDetachRequested()
-    {
-        var worker = new FakeWorker();
-        using var vm = Build(worker);
-        vm.SetTaskId("t1");
-        TaskMonitorViewModel? requested = null;
-        vm.DetachRequested = m => requested = m;
-        vm.DetachCommand.Execute(null);
-        Assert.Same(vm, requested);
-    }
-
     [Fact]
     public void TaskQuestionAsked_SurfacesQuestion()
     {