API TUSSAM

Turns TUSSAM's internal API (no CORS, aggressive rate limiting) into an open service: it normalizes coordinates, caches arrival times (60s TTL) and keeps responding even when the origin is down thanks to single-flight, Retry-After-aware retries and stale-cache fallback. 967 stops and 49 lines in SQLite, nearby-stop search (bbox + Haversine), GeoJSON output ready for Leaflet/MapLibre and a Docker image on ghcr.io.