Set GitHub Action for testing (setup Python using `uv` or similar)

[gvegayon]

[olivia-banks]

This should be pretty simple. We can use the Containerfile as the image for the action, which already has everything we need installed. Then just running a single uv command to make sure Streamlit launches (since we have no tests), should be enough.

[gvegayon]

Sure, we can even use the image stored in ghcr.io