Feature detail (lazy-loaded)

Fetches detailed properties for a feature on demand. For parking-type features (truck_parking, truck_rest_areas, rest_areas, service_plazas, parking) the response also carries availability_trend[] — the per-hour-of-day occupancy trend ({ hour, avg_available, avg_capacity, samples }, hours in UTC) built from recorded live-occupancy history, so a client can answer "is this lot typically full at my ETA?". Empty/omitted until the time series has accumulated for that feature.