Add FoldHourlyRollupsAsync (in-memory grouped, per-metric gauge-last/rate-sum,
idempotent upsert on the series+hour key with null-ScopeKey equality, exclusive
upper hour bound so the in-progress hour is never folded), GetHourlySeriesAsync
(same KpiSeriesPoint contract as GetRawSeriesAsync), and PurgeRollupsOlderThanAsync
(one-hour-sliced batched DELETE mirroring PurgeOlderThanAsync). Adds 7 repo tests.
Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj
Joseph Doherty