Added
- ADS-B → airband audio (#271). Selecting an aircraft now shows a "Tune ATC" button that finds the nearest airport to the aircraft's position and loads its tower/approach/ATIS frequency into the airband receiver, then starts listening. Backed by a bundled OurAirports (public-domain) frequency dataset and a new
/adsb/nearest-airbandlookup. Scope is nearest-airport tower/approach; enroute/centre frequencies and "last heard transmission" are out of scope.