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/slots.ts

@@ -0,0 +1,29 @@
+import {
+  type ElevatorNode,
+  getResolvedElevatorDoorPanelStyle,
+  getResolvedElevatorShaftStyle,
+  type SlotDeclaration,
+} from '@pascal-app/core'
+
+export type ElevatorSlotId = 'cab' | 'doors' | 'shaft' | 'glass'
+
+export const ELEVATOR_CAB_SLOT_DEFAULT = 'library:preset-softwhite'
+export const ELEVATOR_DOORS_SLOT_DEFAULT = 'library:metal-steel'
+export const ELEVATOR_SHAFT_SLOT_DEFAULT = 'library:preset-lightgrey'
+export const ELEVATOR_GLASS_SLOT_DEFAULT = 'library:preset-glass'
+
+export function elevatorSlots(node: ElevatorNode): SlotDeclaration[] {
+  const slots: SlotDeclaration[] = [
+    { slotId: 'cab', label: 'Cab', default: ELEVATOR_CAB_SLOT_DEFAULT },
+    { slotId: 'doors', label: 'Doors', default: ELEVATOR_DOORS_SLOT_DEFAULT },
+    { slotId: 'shaft', label: 'Shaft', default: ELEVATOR_SHAFT_SLOT_DEFAULT },
+  ]
+
+  const hasGlass =
+    getResolvedElevatorShaftStyle(node.shaftStyle) === 'glass' ||
+    getResolvedElevatorDoorPanelStyle(node.doorPanelStyle) === 'glass-frame'
+
+  if (hasGlass) slots.push({ slotId: 'glass', label: 'Glass', default: ELEVATOR_GLASS_SLOT_DEFAULT })
+
+  return slots
+}