* Add catalog-based material presets across structural nodes
* Fix material picker fallback and wall visible highlights
* Preserve wall materials in selection highlights
Stair system (full stack):
- New StairNode + StairSegmentNode schemas with flights, landings, L/U-shapes
- StairSystem: geometry generation with throttled per-frame updates
- Stair tool, edit system, panels, tree node, and renderers
- Event bus types, scene registry, and command palette entries
Scene graph utilities:
- cloneLevelSubtree: deep-clone a level with remapped IDs
- forkSceneGraph: clone + strip scan/guide nodes for project forking
Core improvements:
- Read-only mode on scene store (blocks create/update/delete when locked)
- readOnly guards on node-actions and collection actions
- Upload store for scan/guide file upload handling
Viewer state:
- previewSelectedIds for box-select live preview
- hoverHighlightMode (default/delete) for delete-mode hover outline
- 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
sudhir