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.

CHANGELOG.md

@@ -1,5 +1,16 @@
 # Changelog
 
+- Flights' ground floor works across the antimeridian. The viewer-distance
+  check behind the 150 km floor radius and its copy in the photoreal mesh-floor
+  sampler subtracted longitudes without wrapping, so two points 21 km apart
+  across 180° measured about 38,000 km and low or grounded aircraft just across
+  the line from the viewer were never floored. A contact's display corridor
+  walked a segment across 180° the long way round, spending its cell budget on
+  ground behind the contact, and a contact on the seam lost its cell hysteresis.
+  SEARCH NEARBY SITES on a view across 180° searched Google Places around
+  longitude 0, on the far side of the globe, with a radius sized from the view's
+  height alone; it now searches the view.
+
 - Add Barcelona's bike share to the GBFS registry: Bicing (543 stations, the
   city's PBSC system) and AMBici (237 e-bike stations across the metropolitan
   area, run by nextbike). Both are keyless GBFS 2.3 feeds listed in