fix: retrieve assigned vehicle from Fleet Service in driver planning endpoint
- Add vehicleId field to DriverPlanningDTO response
- Replace VehicleService (local JSON) with FlotService (Fleet Service) for vehicle data
- Add mapToVehicleDTO method to map Fleet Service response to VehicleDTO
- Add findByIdForPlanning query method to optimize database query
- Ensure assignedVehicle contains real vehicle data instead of null