refactor: restructure repo into core/app modules with per-study folders

Reorganize Palladium codebase into a modular architecture with `core/`
shared logic and `app/` Streamlit UI, separating per-study assets into
`studies/YYYYMM_<Vendor>/` folders containing notebooks, seed data, and
configuration. Update README to reflect new structure, add `.gitignore`
entries for `.env` and study exports, and refresh component documentation.

requirements.txt

@@ -0,0 +1,9 @@
+requests>=2.31
+python-dotenv>=1.0
+jupyter>=1.0
+streamlit>=1.30
+pandas>=2.0
+plotly>=5.18
+numpy>=1.26
+pytest>=7.4
+ruff>=0.1