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.

app/pages/_helpers.py

@@ -0,0 +1,28 @@
+"""Common helpers shared by the page modules."""
+
+from __future__ import annotations
+
+import streamlit as st
+
+from core.tei_client import AthenaAPIError, TEIClient
+
+
+def report_meta(client: TEIClient, tool: dict) -> dict:
+    """Fetch the linked report (handles both nested-object and id-only forms)."""
+    report_obj = tool.get("report")
+    if isinstance(report_obj, dict):
+        return report_obj
+    if isinstance(report_obj, str):
+        try:
+            return client.get_report(report_obj)
+        except AthenaAPIError as e:
+            st.error(f"Failed to load report template: {e}")
+    return {}
+
+
+def safe(fn, *args, **kwargs):
+    try:
+        return fn(*args, **kwargs)
+    except AthenaAPIError as e:
+        st.error(f"Athena API error {e.status_code}: {e.detail}")
+    return None