A bare catch {} turned every failure - including an admin-only node with no
historian actor - into 'Loading...' forever, and a tick queued after a sync
timer dispose still issued an Ask. HistorianSinkStatusReader classifies a poll
as Available / NotOnThisRole (permanent: shown once, polling stops) /
Unavailable (shown with the last good status and its read time). The page
follows Fleet.razor: IAsyncDisposable, _disposed, overlap guard, page CTS.
Refs #745
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
1313b94097