Fix glTF interleaved attribute import

[krapnikkk]

Fixes #962

What changed

• Read vertex positions through BufferAttribute.getX/getY/getZ.
• Read UVs and indices through attribute getters.
• Bump gltf_importer to 1.2.1 and rebuild the committed bundle.

Root cause

GLTFLoader creates InterleavedBufferAttribute instances for glTF accessors that share a strided buffer view. Directly indexing .array assumes tightly packed attributes and ignores the interleaved stride and accessor offset, which corrupts vertex positions and UVs. The attribute getters handle both regular and interleaved buffers.

Validation

• npm run build in plugins/gltf_importer/src
• npm run validate gltf_importer
• git diff --check