Read customer pool utilization from retained device hours

Totals cover retained ready-device hourly rows only. Complete means all represented ready seconds have activity evidence, not that the pool existed throughout the requested range. Partial means some ready seconds lack observations and all activity totals and percentages are null. No data means no retained rows. Zero capacity has null percentages. Missing activity is never counted as idle or stranded. Fragmentation, queued and burst are unavailable without Route and remain null in the observe ledger. Route measurements use independent durable queue and execution evidence in the pool summary. Host summaries and host buckets keep Route fields null because these cannot be attributed to a private host.