The project does not include a built-in 3D .glb by default. It expects you to provide one at:

• models/tshirt.glb

You have two ways to supply it:

• Put a GLB file named models/tshirt.glb in the project folder (the app will try to auto-load it).
• Or open the app and use the "Load T-shirt Model" file input in the UI to upload any .glb/.gltf at runtime.

Notes:

• Use a GLB/GLTF with proper UVs so the design texture maps correctly.
• Prefer meshes using MeshStandardMaterial (or convert materials) so color/texture changes work as implemented.