feat(planning): persist and expose hasPassengerAbsent on trip planning slots
Consume hasPassengerAbsent from TripPassengerCountUpdatedDTO and apply it together with passengerCount on both TripPlanning and TripCircuit for the matching tripId and date (including unassigned circuit rows).
Map the flag to DriverTimeSlotDto so driver planning UI can show absence indicators.
Extend updatePassengerCountForTrip and the test passenger-count endpoint to accept and return hasPassengerAbsent for manual verification.