admin/pools: back the 7d traffic window with daily rollups

[masterkain]

Parent: admin/pools async traffic follow-ups

Goal

Replace the slow raw-row 7d Pool traffic aggregation with a daily-rollup-backed path

Acceptance criteria

• read completed UTC days from daily rollups
• merge the still-hot current-day raw tail under the same usage_unknown and settled-cost exclusions
• fall back to the raw path when rollups are late, partial, or unavailable
• preserve existing totals and chart semantics
• add boundary coverage for UTC day edges, fresh deployments, and incomplete backfills
• verify the operator-visible 7d loading time against a realistically populated database