Aircraft draw from GPU icon sets, so the billboard mirror, the billboard
treatment and the aircraft visual-state module had no callers left. 3D models
are now records the layer holds under the contact's id (modelRecord.js):
show and placement are written through showModel/placeModel and read back
from the record; renderer-measured values stay on record.model.
The tracked-model click check only matches when a tracked model exists, so
an id-only pick is never mistaken for a click on the tracked plane.
Sameh Khamis