Measure each live aggregation bucket's own upstream duration server-side
(auth fetch attributed to Work/Activity, per-feed timed gather) and surface
the measured values in the Live data status panel.
- Per-bucket latency_ms measured individually, never batch wall time
- Stale feeds label their number 'last known'; unmeasured feeds say
'not measured' instead of an ambiguous dash; hidden when no data
- Failed buckets keep their last known latency across partial refreshes
- Panel is aria-labelled rows as a list, values wrap on mobile
- Ignore .venv/
