feat: multilingual vectoriser demo notebook

[frayle-ons]

✨ Summary

These Change add a new notebook, images and a dataset to show off multilingual capabilities of the ClassifAI package.

Also added is a small fix to ensure that images in the demo notebooks render correctly on the Github site. It was found that several notebook images didn't reference the current path ./ which is required to display images.

📜 Changes Introduced

• (docs:) new notebook, images for notebook display and demo data
• (fix:) corrected file paths on notebook images to render correctly on GitHub

✅ Checklist

Passes all pre-commit hooks prior to commit and push

🔍 How to Test

Follow the /DEMO/readme.md guide on how to set up the notebook demos. See the new dataset available for the demo at "DEMO/files/vectorstore_2d_vis_multilingual.png" and the notebook itself is: "DEMO/multilingual_datasets_and_vectorisers.ipynb".

Those resources and the instructions should allow the tester to run the notebook locally. If the tester has a local copy of the package repo and has the branch 230 checked out they can also use uv sync --extra huggingface to set up the correct dependencies and venv to run the notebook.