Read-only _is_premium_building(db, house_id) looks up target_house_id in the
premium_houses MV (data/sql/139) and surfaces premium_building +
premium_building_median_ppm2 on AggregatedEstimate. Metadata only for
manual-review routing (#4) — does NOT touch _price_from_inputs / expected_sold /
median / ranges, so the backtest regression gate is unaffected.
MV-missing / SQL errors degrade to (False, None) with a rollback so an estimate
never breaks where the MV does not yet exist.
