Fix deployment on streamlit cloud

[ml-evs]

This hackathon demo is now served at https://yellowhammer.streamlit.app/, but will need some tweaking to work with e.g., the datalab demo deployment. This issue tracks that:

• provide way to give LLM and datalab API keys in UI
• check that image upload etc still works
• update prompt for latest version of datalab-python-api
• general tidying and docs: title and info page in the UI
• Cool stuff: WASM version?