feat(paint-slots): paintable slots for windows + doors (frame/glass, panel/glass)

Windows and doors build all visuals in their viewer systems from module-global
materials, so this threads per-node slot materials + userData.slotId tags
through those builders without restructuring them:

- window: 'frame' + 'glass' slots. door: 'panel' (body = casing + leaf) +
  'glass'; the opening reveal keeps its own material.
- Each system captures per-frame viewer state, then updateWindow/DoorMesh points
  the builder-facing base/glass materials at the node's resolved slot override
  (recomputed per node, so the next node resets without a restore). Meshes are
  auto-tagged in the shared addBox/addShape helpers by which material they got.
- Textures-off still collapses to the role material (escape hatch); a slot
  override only applies in colored mode.
- Editing a referenced scene material re-dirties the window/door (these systems
  aren't covered by GeometrySystem's scene-material re-dirty).
- New paint capabilities (resolve role from userData.slotId, preview by
  userData.slotId) + capabilities.slots; window/door dropped from the paint
  disabled list. Shared previewSlotByUserData helper.

Defaults unchanged: unpainted windows/doors render exactly as before (the slot
fallback is the existing frame/glass material), so no visual regression.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/nodes/src/door/paint.ts

@@ -0,0 +1,17 @@
+import type { PaintResolveArgs } from '@pascal-app/core'
+import { createSlotPaintCapability, previewSlotByUserData } from '../shared/slot-paint'
+
+/**
+ * Door paint on the unified slot model. The door's viewer system tags each built
+ * mesh with `userData.slotId` (`panel` / `glass`), so the role resolves straight
+ * from the pointer hit; commit writes `node.slots[slotId]`.
+ */
+function resolveDoorRole(args: PaintResolveArgs): string | null {
+  const slotId = (args.hitObject?.userData as { slotId?: string | null } | undefined)?.slotId
+  return typeof slotId === 'string' ? slotId : null
+}
+
+export const doorPaint = createSlotPaintCapability({
+  resolveRole: resolveDoorRole,
+  applyPreview: previewSlotByUserData,
+})