feat(layers): add FAA drone restrictions airspace layer

Show US prohibited and restricted special-use airspace from the keyless
FAA SUA FeatureServer as an off-by-default Infrastructure layer, with
share-link token 3 and an informational-only disclaimer.

src/data/layerStateTokenReservations.json

@@ -6,6 +6,7 @@
   ["bikeshare", "b"],
   ["cctv", "c"],
   ["directions", "n"],
+  ["drone-airspace", "3"],
   ["earthquakes", "e"],
   ["fire-perimeters", "2"],
   ["flights", "f"],