feat: Add catalog-based material presets across structural nodes

[sudhir9297]

Added a shared, catalog-based material ( 13 items ) preset system across wall, slab, roof, roof-segment, stair, stair-segment, ceiling, and fence.

Key updates:

• node-type filtered material picker
• custom material fallback
• preset refs stored as library:<id>
• viewer resolves presets via maps + mapProperties
• textured materials now supported in the shared flow

Rendering/runtime fixes:

• async + cached texture loading to prevent rapid-switch crashes
• correct color-space handling for albedo vs data maps
• AO support for wall and fence UVs
• walls/slabs keep their real material instead of blue highlight overrides
• fixed post-processing fallback so it doesn’t render before WebGPU init

[open-pascal]

Rechecked the follow-up commits against the two regressions I called out earlier.

• The door/window material panel is no longer blank: MaterialPicker now keeps a custom fallback even when there are no catalog items.
• Visible wall selection/delete highlighting is restored in wall-cutout.tsx, and the highlighted variants now preserve the underlying wall material/preset appearance.

So the two blockers from my earlier review look addressed from my side. One smaller note remains: door/window are effectively custom-only now, instead of exposing the old preset swatches, but that is separate from the blank-state regression I flagged.