feat(ui): mission-control pane title shows usage limit reset time

When a list-handler handoff is deferred waiting for the 5h usage limit to
reset, the Mission Control pane title is augmented with ⏳ waiting for
limit reset (HH:mm) so the wait is visible at a glance. Extends
HubBroadcaster.HandoffRequested with an optional deferredUntil DateTime
parameter, wired through SignalR to MissionControlViewModel, which formats
it into the pane title via Loc.T(missionControl.waitingForLimitReset).

src/ClaudeDo.Worker/External/HandoffMcpTools.cs

@@ -92,6 +92,8 @@ public sealed class HandoffMcpTools
             taskId, survivingTaskIds, round.EffectivePhase, cancellationToken);
         if (deferredUntil is null)
             await _broadcaster.HandoffRequested(taskId, survivingTaskIds, round.EffectivePhase);
+        else
+            await _broadcaster.HandlerHandoffDeferred(taskId, deferredUntil.Value);
 
         return new HandoffListHandlerResult(
             true, taskId, task.Number, survivingTaskIds.Count, round.EffectivePhase, round.Coerced, deferredUntil);