Wire the posix-sdc dependency as a triplet:
- pyproject declares the abstract posix-sdc[hub], so the trainer's --hub path can
reach the Hub (huggingface_hub) wherever sekft is installed;
- Pipfile [packages] pulls the published wheel from the private index;
- Pipfile [dev-packages] pulls the git develop branch for develop-time work.
Commit Pipfile.lock so the dependency surface and its lock land together.
