Fix: gltf/glb textures not loading

[chrismichaelps]

I spent way too much time debugging this, but here's what was happening:

• The textures weren't showing at all - Turns out we were missing a tiny but crucial line in our material shaders (outputs:surface declaration).
• When textures did show, they looked weird - The UV coordinates were all messed up, going way outside the normal 0-1 range.
• The texture mapping was flipped - USDZ uses a different coordinate system than regular GLTF files.
• The model hierarchy was wrong - Materials weren't properly connected to the geometry.

Fixed the Model Hierarchy

• Materials are now properly connected to the geometry nodes.
• Embedded geometry approach - Instead of separate files, everything is in one place.
• Proper material binding - Materials actually stick to the right parts of the model.
• Cleaner structure - Materials are organized under /Root/Materials for better compatibility.

Made Everything More Robust

• Auto-detect if textures are JPEG or PNG (instead of assuming PNG).
• Generate better texture IDs based on actual content.
• Embed geometry data directly instead of separate files (simpler = better).