feat(paint-slots): migrate elevator onto the unified slot model

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>

packages/nodes/src/elevator/definition.ts

@@ -13,7 +13,9 @@ import {
 import { buildElevatorFloorplan } from './floorplan'
 import { elevatorResizeAffordance, elevatorRotateAffordance } from './floorplan-affordances'
 import { elevatorParametrics } from './parametrics'
+import { elevatorPaint } from './paint'
 import { ElevatorNode } from './schema'
+import { elevatorSlots } from './slots'
 
 const SIDE_HANDLE_OFFSET = 0.22
 const HEIGHT_HANDLE_OFFSET = 0.3
@@ -223,6 +225,8 @@ export const elevatorDefinition: NodeDefinition<typeof ElevatorNode> = {
     },
     duplicable: true,
     deletable: true,
+    slots: (node) => elevatorSlots(node as ElevatorNodeType),
+    paint: elevatorPaint,
   },
 
   parametrics: elevatorParametrics,