feat(13): reference posix-sdc three ways for seamless multi-machine dev

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.

pyproject.toml

@@ -31,7 +31,7 @@ classifiers = [
   "Typing :: Typed",
 ]
 dependencies = [
-  "tiararodney.posix-sdc",
+  "tiararodney.posix-sdc[hub]",
 ]
 dynamic = ["version"]
 requires-python = ">=3.9"