fix: replace deprecated use_container_width with width='stretch

[saurabh12nxf]

Summary

Removes all uses of the deprecated use_container_width parameter
across the prototype, replacing with the new width="stretch" API.

Motivation

Streamlit deprecated use_container_width for removal after 2025-12-31.
The Streamlit server was logging deprecation warnings on every page load:

Please replace `use_container_width` with `width`.
`use_container_width` will be removed after 2025-12-31.
For `use_container_width=True`, use `width='stretch'`.

Changes

• prototype/Home.py: 1 st.plotly_chart call
• prototype/visualizations/ui_components.py: 4 st.button + 1 st.plotly_chart calls

References

• Streamlit changelog
• Consistent with the pattern already used in prototype/pages/IQB_Map.py
  (which uses width="stretch" and width="stretch" for dataframes)

[bassosimone]

A-ha, good catch! I will take a more in depth look, but this feels like a surgical improvement. Thanks!

[bassosimone]

After listing our project for GSoC, we received a large amount of pull requests across several repositories. We are dealing with the backlog, but this would take time. We will get back to this pull request eventually. In the meanwhile, if you are a GSoC applicant, please read our updated GSoC policy: https://github.com/m-lab/gsoc/.