feat(paint-slots): concrete-plate finish + try defaults (wall=concrete, slab=wood plank 48, ceiling=soft white)

- material-library: add 'concrete-plate' KTX2 finish (512, fabric/leather-style
  pipeline) + editor-app texture mirror.
- viewer: shared resolveSlotDefaultMaterial(colour|library ref) so a kind's slot
  default can be a catalog finish, not just a flat colour.
- wall default -> library:concrete-plate (interior + exterior).
- slab default -> library:wood-woodplank48 (slab geometry resolves it via the
  shared helper).
- ceiling default -> soft white #f2eee6 (ceiling renders flat-tinted).

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

packages/nodes/src/slab/geometry.ts

@@ -8,9 +8,10 @@ import {
   generateSlabGeometry,
   type RenderShading,
   resolveMaterialRef,
+  resolveSlotDefaultMaterial,
 } from '@pascal-app/viewer'
 import { FrontSide, Group, type Material, Mesh, type Texture } from 'three'
-import { SLAB_SLOT_DEFAULT_COLOR } from './slots'
+import { SLAB_SLOT_DEFAULT } from './slots'
 
 /**
  * Stage B builder for slab. Reuses `generateSlabGeometry` (pure
@@ -62,8 +63,8 @@ function getSlabMaterial(
     return getLegacySlabMaterial(node, shading)
   }
 
-  // Declared slot default (visual parity with the retired DEFAULT_SLAB_MATERIAL).
-  return createDefaultMaterial(SLAB_SLOT_DEFAULT_COLOR, 0.8, shading)
+  // Declared slot default — a catalog `library:` finish or a flat colour.
+  return resolveSlotDefaultMaterial(SLAB_SLOT_DEFAULT, shading, 0.8)
 }
 
 function getLegacySlabMaterial(node: SlabNode, shading: RenderShading): Material {
@@ -83,7 +84,7 @@ function getLegacySlabMaterial(node: SlabNode, shading: RenderShading): Material
     ? createDefaultMaterial('#ffffff', 0.5, shading)
     : node.material
       ? createMaterial(node.material, shading).clone()
-      : createDefaultMaterial(SLAB_SLOT_DEFAULT_COLOR, 0.8, shading)
+      : createDefaultMaterial('#e5e5e5', 0.8, shading)
 
   if (preset) {
     applyMaterialPresetToMaterials(material, preset)

packages/nodes/src/slab/slots.ts

@@ -2,10 +2,12 @@ import type { SlotDeclaration } from '@pascal-app/core'
 
 export type SlabSlotId = 'surface'
 
-// Visual parity with the retired DEFAULT_SLAB_MATERIAL (light grey).
-export const SLAB_SLOT_DEFAULT_COLOR = '#e5e5e5'
+// Declared default appearance for an unpainted slab surface in colored mode —
+// a catalog `library:<id>` finish or a `#rrggbb` colour. Textures-off collapses
+// to the themed floor role (the escape hatch).
+export const SLAB_SLOT_DEFAULT = 'library:wood-woodplank48'
 
 /** A slab exposes a single paintable floor surface. */
 export function slabSlots(): SlotDeclaration[] {
-  return [{ slotId: 'surface', label: 'Surface', default: SLAB_SLOT_DEFAULT_COLOR }]
+  return [{ slotId: 'surface', label: 'Surface', default: SLAB_SLOT_DEFAULT }]
 }