fix(geo): wrap longitude differences across the antimeridian

The flights ground-floor pipeline subtracted longitudes without wrapping.
approxDistanceKm, and its copy in the mesh-floor sampler, measured two
points 0.2° apart either side of 180° (21 km at Fiji) as about 38,000 km,
so low and grounded aircraft just across the line from the viewer were
never floored or mesh-sampled. corridorFloorCells walked a segment across
180° the long way round, filling its cell budget with ground behind the
contact and never requesting the cells it was about to cross, and
stickyFloorCell dropped its hysteresis for a contact on the seam. Each now
takes the short way round, and corridor points are normalised back into
[-180, 180].

SEARCH NEARBY SITES centred its Google Places search on the mean of west
and east, which for a view across 180° (west > east) is longitude 0, and
sized the radius from the view's height alone. It now measures the view's
width through 180° and searches its real centre.

src/services/meshFloorSampler.js

@@ -84,8 +84,11 @@ export function createMeshFloorSampler({
    */
   function _approxKm(lat1, lon1, lat2, lon2) {
     const dLat = (lat2 - lat1) * 111.32;
+    // The short way round, so points either side of 180° stay close.
+    let dLonDeg = lon2 - lon1;
+    dLonDeg -= 360 * Math.round(dLonDeg / 360);
     const dLon =
-      (lon2 - lon1) * 111.32 * Math.cos((((lat1 + lat2) / 2) * Math.PI) / 180);
+      dLonDeg * 111.32 * Math.cos((((lat1 + lat2) / 2) * Math.PI) / 180);
     return Math.hypot(dLat, dLon);
   }