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.

pyproject.toml

@@ -0,0 +1,49 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "palladium"
+version = "0.1.0"
+description = "TEI (Total Economic Impact) Calculator — Palladium"
+readme = "README.md"
+requires-python = ">=3.11"
+license = {file = "LICENSE"}
+authors = [{name = "NTT Data"}]
+dependencies = [
+    "requests>=2.31",
+    "python-dotenv>=1.0",
+    "pandas>=2.0",
+    "plotly>=5.18",
+    "numpy>=1.26",
+]
+
+[project.optional-dependencies]
+notebooks = ["jupyter>=1.0", "ipython>=8.0"]
+app = ["streamlit>=1.30"]
+dev = ["pytest>=7.4", "ruff>=0.1"]
+
+[project.scripts]
+palladium = "core.cli.main:main"
+
+[tool.setuptools.packages.find]
+include = ["core*", "palladium*"]
+exclude = ["tests*", "studies*", "app*", "docs*"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+addopts = "-q"
+
+[tool.ruff]
+line-length = 100
+target-version = "py311"
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "B", "UP", "W"]
+ignore = ["E501"]  # line length handled by formatter
+
+[tool.ruff.lint.per-file-ignores]
+"studies/*/notebooks/*.ipynb" = ["E402"]
+"tests/*" = ["F401"]
+"app/main.py" = ["E402"]  # sys.path bootstrap before app imports