fix(infrastructure): test the ground, not the ellipsoid, for in-view sampling

An unsampled base sits at ellipsoid height 0. Over high terrain seen at an
angle that point projects below the screen while the ground above it is in
view, so the gate skipped ground the camera could see and never sampled it.
The gate now tests loaded globe terrain when there is some, and otherwise
the whole span of heights a sample can accept (0 to 9,000 m).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

changelog.d/1464-infrastructure-ground-sample-in-view.md

@@ -1,4 +1,4 @@
-- Ground-sample Data Centers and Dams markers only when the camera sees their
-  base. An off-screen base read through the Earth and retried every 2 s, which
-  held the page near 2 s a frame over Ashburn, Virginia on the Esri map
+- Ground-sample Data Centers and Dams markers only when the camera sees the
+  ground under them. Unseen ground read through the Earth and retried every
+  2 s; over Ashburn, Virginia on the Esri map, slow frames reached 2 s
   (quanticsoul4772, #1464).