Add refresh_data script and startup script for offline data setup

- Introduced `scripts/refresh_data.py` to download UNRATE and WTI data from FRED and store it in a SQLite database.
- Added `startup.sh` script to set up a Python virtual environment and install dependencies for offline use.
- Updated `repo-context.txt` to reflect the new scripts and their purposes.

scripts/refresh_data.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+"""
+refresh_data.py
+---------------
+Download UNRATE and DCOILWTICO from FRED and store them in SQLite
+(data/fred.db).  Run on a connected machine; commit the DB afterwards.
+"""
+
+from datetime import date
+import pathlib
+import sqlite3
+
+import pandas as pd
+from pandas_datareader.data import DataReader
+
+HERE = pathlib.Path(__file__).resolve().parent
+DATA_PATH = HERE.parent / "data"
+DB_FILE = DATA_PATH / "fred.db"
+
+START = "1948-01-01"          # earliest UNRATE observation
+END = date.today().isoformat()
+SERIES = ("UNRATE", "DCOILWTICO")
+
+
+def main() -> None:
+    DATA_PATH.mkdir(exist_ok=True)
+    with sqlite3.connect(DB_FILE) as conn:
+        for s in SERIES:
+            print(f"↯ downloading {s} …")
+            df = DataReader(s, "fred", START, END)
+            df.to_sql(s, conn, if_exists="replace", index_label="date")
+            print(f"✓ wrote {s}: {len(df):,} rows")
+    print(f"\nDone.  SQLite DB at {DB_FILE} ({DB_FILE.stat().st_size/1024:.0f} KB)")
+
+
+if __name__ == "__main__":
+    main()