DeleteTaskAsync had no IsConnected guard, unlike every other worker-dependent
command in DetailsIslandViewModel, so an offline delete was a silent no-op.
WorkerClient.DeleteTaskAsync also only caught HubException, letting the
InvalidOperationException thrown by an inactive hub connection escape into
the unobserved command task and vanish.
Gate DeleteTaskCommand behind CanDeleteTask (Task != null && IsConnected),
re-evaluate it on connection-state changes, widen WorkerClient to catch the
connection-inactive case too, and wrap the ViewModel's call in try/catch as
a second line of defense against a race between the guard and the call.
mika kuns
a78cc526a6