```unzip_ckpt.py``` fails with "not a valid zip file" — checkpoint clone downloads Git LFS pointer files instead of actual zips

[mlshehab]

Issue

Following the README's Download Fine-tuned VLA/VLM Checkpoints section:

​bash git clone git@hf.co:Yinpei/pi05_baseline runs/ckpts/pi05_baseline uv run ./scripts/unzip_ckpt.py runs/ckpts ​

fails with:

​ Found 1 zip files under .../runs/ckpts [bad] .../runs/ckpts/pi05_baseline/pi05_baseline/79999.zip is not a valid zip file ​

Cause

If git-lfs is not installed (or not initialized) on the machine, the clone
succeeds but only downloads the LFS pointer files (~136 bytes) instead of
the actual checkpoint zips:

​bash $ ls -lh runs/ckpts/pi05_baseline/pi05_baseline/79999.zip -rw-rw-r-- 1 user user 136 Jul 1 16:16 79999.zip ​

unzip_ckpt.py then correctly reports the file as an invalid zip. This is
easy to hit since the install instructions use GIT_LFS_SKIP_SMUDGE=1, so
nothing earlier in the setup surfaces a missing git-lfs.

Note that installing git-lfs afterwards and running git lfs pull may still
fail: LFS fetches objects over HTTPS by default (password auth is deprecated
on HF), and pointing lfs.url at SSH requires the machine's SSH key to be
linked to a Hugging Face account.

Fix / suggestion

The most robust path that avoids both problems is huggingface-cli:

​bash uv run huggingface-cli download Yinpei/pi05_baseline --local-dir runs/ckpts/pi05_baseline ​

Suggestion: add a note in the Download section to either (a) install and
initialize git-lfs (sudo apt install git-lfs && git lfs install) before
cloning checkpoints, or (b) recommend huggingface-cli download as the
default method. A size sanity check in unzip_ckpt.py that detects LFS
pointer files and prints a helpful hint would also save people time.
​```