Prevent Blender from overwriting raw Trellis GLB file

Fix glTF binary corruption in Blender export scripts

Use non-destructive fast cleanup for FBX export to preserve original UV mapping, materials, and textures without distortion

Fix EXT_texture_webp GLB import error in Blender by upgrading to Blender 4.2 LTS and sanitizing glTF extension headers

Restructure repository layout: move server and scripts to backend/ and web assets to frontend/ (ignore database and generated outputs)