fix(cctv): on a globe map the camera plane ends where the view meets the ground

The activation probe raycast only the photoreal tiles. On a globe map the ray
missed, or ran on through the Earth and met a primitive thousands of
kilometres away, and the monitor plane stood at the camera's full range:
about a kilometre wide and hundreds of metres up. A hit at or beyond the range
now counts as none, and on a globe map the plane also clamps short of the
globe's terrain along the axis, or flat ground at the mount's ground while
that terrain is still loading, whichever is nearer.

src/data/cctv.js

@@ -29,6 +29,7 @@ export const writeCalibrationStoreV2 = layer.writeCalibrationStoreV2;
 export const deriveCalBadge = layer.deriveCalBadge;
 export const computeFrustumGeometry = layer.computeFrustumGeometry;
 export const activationProbeClampRange = layer.activationProbeClampRange;
+export const flatGroundAxisDistance = layer.flatGroundAxisDistance;
 export const frameSignatureFromPixels = layer.frameSignatureFromPixels;
 export const _createCctvProjectionPlaneForTest =
   layer._createCctvProjectionPlaneForTest;