The ceiling renderer was falling back to DEFAULT_CEILING_MATERIAL (an
opaque MeshStandardMaterial) when no material was set on the node.
This made ceilings fully opaque instead of using the intended
transparent grid pattern for scenes created before v0.3.2.
Now uses resolveMaterial() to extract the color from whatever material
config exists (preset, custom, or default white), then always creates
the proper transparent ceiling materials for both faces.
Pascal
b6636c179b