[Weather] openmeteo_fallback (default false, only with weather_provider = noaa) answers wx from Open-Meteo when NWS reports a point as outside its coverage (HTTP 400/404 from /points), in gwx's format and labels and wx's units. Timeouts and server errors keep today's error. The point goes into the existing NWS no-coverage cache, so later requests skip NWS for 24 hours. wx <place> alerts there replies that alerts are not available.
gwx's per-point body moves into _weather_for_point so wx can reuse it without geocoding twice; gwx's output is unchanged.
