refactor(geo): define shared distance contract

src/data/regionalModel.js

@@ -1,3 +1,5 @@
+import { greatCircleMeters } from '../geoDistance.js';
+
 const MAX_ARTICLES = 5;
 
 function cleanText(value, maxLength = 180) {
@@ -136,19 +138,8 @@ export function weatherCodeLabel(code) {
 
 /** Great-circle distance used to avoid refetching a regional brief every animation frame. */
 export function regionalDistanceM(from, to) {
-  if (
-    ![from?.latitude, from?.longitude, to?.latitude, to?.longitude].every(
-      Number.isFinite,
-    )
-  ) {
-    return Infinity;
-  }
-  const phi1 = (from.latitude * Math.PI) / 180;
-  const phi2 = (to.latitude * Math.PI) / 180;
-  const deltaPhi = ((to.latitude - from.latitude) * Math.PI) / 180;
-  const deltaLambda = ((to.longitude - from.longitude) * Math.PI) / 180;
-  const a =
-    Math.sin(deltaPhi / 2) ** 2 +
-    Math.cos(phi1) * Math.cos(phi2) * Math.sin(deltaLambda / 2) ** 2;
-  return 6371000 * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
+  return greatCircleMeters(
+    { lat: from?.latitude, lon: from?.longitude },
+    { lat: to?.latitude, lon: to?.longitude },
+  );
 }