Elevator exposes four finish slots — cab / doors / shaft / glass (glass only
when shaft or door style is glass) — on node.slots. The finish materials now
resolve through a per-node material set (context provider) keyed on node.slots
+ scene materials: textures-off joinery role -> node.slots ref -> declared
default (cab preset-softwhite, doors metal-steel, shaft preset-lightgrey,
glass preset-glass), with glass transparency flags re-applied. Cab/door/shaft/
glass meshes tag userData.slotId; buttons, indicators, control panels, and
queue strips stay untagged (functional UI, not paintable). Interaction system
untouched. Monochrome unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
