Public data-quality report: live fill rate for EVERY output attribute, measured across every active listing — no API key required

Returns attributes: an ordered list of {label, field, fill_pct} for all 33 output attributes (VIN, Model year, Make, Model, Trim, Condition, Demo, Certified, Mileage, Price, Initial price, Days on market, Exterior/Interior color, Body type, Doors, Passengers, Size class, Powertrain, Drivetrain, Engine size, Transmission, Fuel type, seller name/address/city/province/postal/country/lat/lng, Is cross-listed, Phone). Also fill_rates_pct (flat slug→pct map), listings_measured, data_refreshed_at, and methodology. Condition, Demo, Certified, Is cross-listed and Country are 100% by derivation.