fix(globe): keep the Navara camera above the ground

Navara 0.2.1's camera controller has no terrain or tile collision; its
only zoom limit, minimumZoomDistance, is a distance from the Earth's
centre, so a wheel zoom near the ground went through it (to -5.9 km).

groundFloor.js runs on the engine's preRender after the camera model
reads Navara's camera. While the camera is free (no flight, no lookAt
target) and below 20 km it samples the ground under it (tiles, else
terrain, else the ellipsoid; at most every 250 ms or 20 m), feeds
Navara's clamp (minimumZoomDistance = geocentric radius of the ground
point + 30 m, sent on changes over 10 m, reset to Navara's default
during flights and above 20 km) so the wheel stops smoothly, and lifts a
camera still below ground + 30 m straight up without camera.commanded.
It only lifts, so it cannot oscillate with the shell's ground guard,
whose lift is a flight the floor stands aside for.

scripts/package-boundaries.json

@@ -1764,6 +1764,7 @@
       "src/globe/navara/cameraModel.js",
       "src/globe/navara/createNavaraEngine.js",
       "src/globe/navara/credits.js",
+      "src/globe/navara/groundFloor.js",
       "src/globe/navara/index.js",
       "src/globe/navara/input.js",
       "src/globe/navara/internals.js",