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.

tests/conftest.py

@@ -0,0 +1,32 @@
+"""Pytest fixtures for Palladium tests."""
+
+from __future__ import annotations
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+
+@pytest.fixture(autouse=True)
+def _env(monkeypatch):
+    """Default test env vars so TEIClient() doesn't need a real .env."""
+    monkeypatch.setenv("ATHENA_BASE_URL", "https://athena.test")
+    monkeypatch.setenv("ATHENA_API_KEY", "test-key")
+
+
+@pytest.fixture
+def amazon_connect_seed():
+    """Load the Amazon Connect study's seed data."""
+    sys.path.insert(0, str(ROOT / "studies" / "202602_AmazonConnect"))
+    try:
+        import seed_data  # type: ignore[import-not-found]
+        return seed_data
+    finally:
+        # Leave the path alone — many tests will use the seed
+        pass