Add haversineKm helper and filterStrikesWithinKm filter in
src/lib/api/lightning.js. PrecipitationRadar now filters strikes by
distance from the current location before projecting them, so only
strikes within 25 miles render. No data-source change; relay-down
behavior is unchanged.
Fixes an incorrect haversine expectation in the test (0.3567 deg of
latitude ~= 39.66 km, not 25.7 km).
hermes-explorigin
86acc56143