refactor: move sam_3d_body inside avatar/ for cleaner structure, resolve via PYTHONPATH

fix: restore sam_3d_body as top-level package, clean avatar module, upgrade Dockerfile to pytorch devel base

fix: install sam_3d_body from source + lazy avatar imports to prevent crash

fix: add zstd required by Ollama install script

fix: add missing system build deps for pycocotools and pyrender

Initial clean commit with LFS for Hugging Face