Renderer improvements:
- Configure shadow camera frustum to cover full house (was default -5..5)
- Add geometry and material caching to reduce GPU allocations
- Add proper disposal of Three.js objects on floor switch (fix memory leak)
- Add error handling for fetch failures with custom event dispatch
- Add room labels as sprites floating in each room
- Support wall-mounted furniture Y positioning via position.y
- Use cached highlight materials instead of mutating shared materials