Browse the durable per-run record of lobby state.
Complements AdminLive.Logs rather than replacing it: logs are a live tail of
an in-memory ring buffer, this is history you can still read tomorrow.
Diffs are computed only for the snapshot the reader expanded. Reconstructing state walks every snapshot up to that point, so diffing the whole timeline eagerly would be quadratic in a run's length for a view where one row is usually the interesting one.