nodeMarkers map in live.js grew unbounded because ADVERT-injected
nodes were never removed. Added time-based pruning using health
thresholds from roles.js (24h for companions/sensors, 72h for
repeaters/rooms). Prune interval runs every 60 seconds.
- Track _liveSeen timestamp on each nodeData entry
- Update timestamp on every ADVERT (new or existing node)
- pruneStaleNodes() removes nodes exceeding silentMs threshold
- 5 new tests verifying pruning logic and threshold behavior
- Cache busters bumped
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>