An uncertified reference floor let any automatic support win, however
deep. On Fracture a whole-map mesh 58 m below the ground was the only
automatic support over a tenth of the floor, so the eye sat underground
and every wall and crate blocked it; Breeze, Icebox and Pearl had smaller
pits and volumes doing the same. A support more than 3 m beneath a clear
reference floor now needs to meet the ground somewhere on or beside its
footprint, which keeps rooms under bridges (found at their doorway) and
passages whose reference eye is walled in, and rejects the void.

Also adds tool/svg_height_map_audit_test.dart, a whole-map audit of the
bundled models that renders overlays and counts level jumps, ledges that
block from above, tall stroke pieces beside slopes, and buried or
elevated automatic levels.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>