Cleanup

[will-fawcett-trillium]

Code cleanup and hygiene improvements:

• Remove ~2,100 lines of dead code: delete old/deprecated Streamlit app versions (app_old_1.py, app_old_2.py,
  supermag_web_deployment_old_.py, data_sources_old_.py) and unused generate_data.py
• Replace hardcoded paths with argparse in SHEATH training and inference scripts (sheath_inference.py, sheath_train_best_model.py,
  sheath_train_embeddings.py, sheath_feature_vector*.py), making them runnable outside the original dev environment
• Fix broken imports: consolidate duplicated utility functions into sheath2024 package (new init.py) and update all call sites
• Improve documentation: expand README with project overview, architecture diagram, structure guide, and acknowledgements; tighten
  docstrings across scripts
• Add public quickstart notebook (public/sheath_inference_quickstart.ipynb) for running SHEATH inference end-to-end
• Clear notebook outputs and apply formatting for lint compliance
• Bump minimum Python version from 3.10 to 3.11