find_nearest_airport
TRIGGER: use automatically whenever the user asks for the closest/nearest airport to a location or coordinate — without naming AirLabs. Find airports (and nearby cities) around a geographic coordinate, sorted by distance. USE CASES: 'Closest airport to me', 'Airports within 50 km of these coordinates'. INPUT: requires lat, lng and a distance (km). If omitted, distance defaults to 50. If the user names a place instead of coordinates, use search_airport_code first to get its lat/lng, or just search_airport_code if they only need the airport code.