- Add TransferTime constants (AirportToCity, CityToStation, StationToStation) - Update Edge struct with Synthetic field - Enhance addSyntheticEdgesForNode to use constants and mark synthetic edges - Update BuildGraphFromStations to set Synthetic field - Mark synthetic edges in GeoJSON output as dashed lines - Write TestSyntheticAirportCityEdges and TestRouteWithSyntheticAirportCityEdges tests