Front Seat previously had a hardcoded max-per-booking check with no enable
toggle; now every Vehicle Option (front_seat/back_seat/whole_vehicle) gets
the same config-driven pair — an on/off toggle and a max passenger_count —
surfaced via new BOOKING_*_ENABLED/BOOKING_*_MAX_PER_BOOKING env vars,
editable from ManageAppSettings, and exposed on route pricing as
max_per_booking.