Replace the per-row rawMeasurements dump with DAY/WEEK/MONTH bucket
means read from measurement_rollups. The legacy shape blew past
Codex's 10 MB string limit on power-user accounts; the bucketed shape
stays O(types × buckets) regardless of row count.
Enforce a 5 MB ceiling on the serialised payload; the generate route
downgrades to the aggregated shape and annotates when the cap trips so
future regressions surface in logs.
