feat(paint-slots): round-2 feedback — fence 2 slots + UVs, roof defaults, stair body

- fence: split into two paint slots — panel (posts/base/infill, default charcoal)
  and rail (cap, default wood-finewood27) — as separate meshes with userData.slotId.
  Fix applyFenceUVs to continuous world-space 1 UV unit = 1 m (drop the per-part
  min origin that broke tiling across parts). New generateFenceSlotGeometries.
- roof: real catalog defaults for the segment surfaces via getRoofMaterialArray
  (the actual default path): wall/trim concrete-plate (matches walls), deck +
  soffit soft-white, shingle terracotta; textures-off role escape hatch kept.
  Align nodes getRoofMaterials no-parent fallback to match.
- stair: body slot default -> preset-lightgrey.
- (biome formatting normalization of the round-1 merged renderer files rides along.)

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

packages/viewer/src/systems/roof/roof-materials.ts

@@ -10,8 +10,20 @@ import {
   createMaterialFromPresetRef,
   createSurfaceRoleMaterial,
   type RenderShading,
+  resolveSlotDefaultMaterial,
 } from '../../lib/materials'
 
+// Declared catalog defaults for an unpainted roof, per the 4-slot layout
+// (0 wall/trim · 1 deck · 2 interior soffit · 3 shingle top). The wall/trim
+// band mirrors the wall kind's default (WALL_SLOT_DEFAULT = concrete-plate) so
+// a roof reads as continuous with the walls below it.
+const ROOF_DEFAULT_REFS: [string, string, string, string] = [
+  'library:concrete-plate',
+  'library:preset-softwhite',
+  'library:preset-softwhite',
+  'library:roof-terracottatiles',
+]
+
 export type RoofMaterialArray = [THREE.Material, THREE.Material, THREE.Material, THREE.Material]
 
 const roofMaterialArrayCache = new Map<string, RoofMaterialArray>()
@@ -77,30 +89,42 @@ export function getRoofMaterialArray(
     roofMaterial,
   ]
 
+  // Textures-off (monochrome) is the guaranteed escape hatch: themed role
+  // colours, no catalog finishes.
   if (!textures) {
     roofMaterialArrayCache.set(cacheKey, roleArray)
     return roleArray
   }
 
+  // Textures-on default appearance: catalog finishes per slot (terracotta
+  // shingle, soft-white deck/soffit, wall-coloured trim). Used both when the
+  // roof is unpainted and to fill any individual unpainted slot below.
+  const defaultArray: RoofMaterialArray = [
+    resolveSlotDefaultMaterial(ROOF_DEFAULT_REFS[0], shading),
+    resolveSlotDefaultMaterial(ROOF_DEFAULT_REFS[1], shading),
+    resolveSlotDefaultMaterial(ROOF_DEFAULT_REFS[2], shading),
+    resolveSlotDefaultMaterial(ROOF_DEFAULT_REFS[3], shading),
+  ]
+
   const topMaterial = createResolvedMaterial(top.material, top.materialPreset, shading)
   const edgeMaterial = createResolvedMaterial(edge.material, edge.materialPreset, shading)
   const wallMaterial = createResolvedMaterial(wall.material, wall.materialPreset, shading)
 
   if (!(topMaterial || edgeMaterial || wallMaterial)) {
-    roofMaterialArrayCache.set(cacheKey, roleArray)
-    return roleArray
+    roofMaterialArrayCache.set(cacheKey, defaultArray)
+    return defaultArray
   }
 
-  // Each slot resolves to its own role only, then the themed default — never
+  // Each slot resolves to its own role only, then the declared default — never
   // another role. Cross-role fallback here used to splatter a single painted
   // surface (e.g. the edge) across the shingle and soffit slots. The legacy
   // catch-all still fills every role because `getEffectiveRoofSurfaceMaterial`
   // returns it for top/edge/wall alike.
   const materialArray: RoofMaterialArray = [
-    edgeMaterial ?? roofMaterial,
-    wallMaterial ?? ceilingMaterial,
-    wallMaterial ?? ceilingMaterial,
-    topMaterial ?? roofMaterial,
+    edgeMaterial ?? defaultArray[0],
+    wallMaterial ?? defaultArray[1],
+    wallMaterial ?? defaultArray[2],
+    topMaterial ?? defaultArray[3],
   ]
 
   roofMaterialArrayCache.set(cacheKey, materialArray)