gaussianSplat importer

Claims loose .spz (Niantic) and .ply (3DGS) capture files and wraps each into a .gaussianSplat asset, moving the capture inside so its origin is never lost.

captures/room.spz  →  captures/room.gaussianSplat/
                        room.spz      the capture (the primary)
                        .metadata     count, bounds, SH degree, convention

The capture is decoded once during the import to record what it holds. That decode is also the claim test: a .ply that is an ordinary mesh fails it and the import errors rather than producing an asset that cannot draw, so this importer does not quietly swallow every .ply written to the world.

A capture already sitting inside a .gaussianSplat/ is that asset's own moved-in source and is never re-claimed.