feat: add material system for all node types

- Add MaterialSchema with 10 presets (white, brick, concrete, wood, glass, metal, plaster, tile, marble, custom)
- Add material field to Wall, Slab, Door, Window, Ceiling, Roof, RoofSegment nodes
- Create MaterialPicker UI component with preset selection and custom properties
- Update all renderers to support material rendering with caching
- Add Material section to all node panels (WallPanel, SlabPanel, DoorPanel, WindowPanel, CeilingPanel, RoofPanel, RoofSegmentPanel)
- Update AGENTS.md with Material System documentation

packages/viewer/src/index.ts

@@ -1,6 +1,18 @@
 export { default as Viewer } from './components/viewer'
 export { ASSETS_CDN_URL, resolveAssetUrl, resolveCdnUrl } from './lib/asset-url'
 export { SCENE_LAYER, ZONE_LAYER } from './lib/layers'
+export {
+  clearMaterialCache,
+  createDefaultMaterial,
+  createMaterial,
+  DEFAULT_CEILING_MATERIAL,
+  DEFAULT_DOOR_MATERIAL,
+  DEFAULT_ROOF_MATERIAL,
+  DEFAULT_SLAB_MATERIAL,
+  DEFAULT_WALL_MATERIAL,
+  DEFAULT_WINDOW_MATERIAL,
+  disposeMaterial,
+} from './lib/materials'
 export { default as useViewer } from './store/use-viewer'
 export { InteractiveSystem } from './systems/interactive/interactive-system'
 export { snapLevelsToTruePositions } from './systems/level/level-utils'