feat(data): EUR/USD M1 fetch + daily realized-vol prep (toy slice, #2/#11)

fetch_data.py politely pulls EUR/USD M1 from histdata.com (maintained package
handles the anti-hotlink token; per-year, spaced). prepare_data.py (LOCKED per
Phase-1 contract) parses M1 -> daily series with realized_vol = the val_vol_r2
target (sqrt sum of squared intraday returns). Verified on 2019-2021: 937 days,
March-2020 COVID RV spike 5.1x over 2019 median — real signal, target works.
Data gitignored (DVC/MinIO = #10).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/fetch_data.py

@@ -0,0 +1,31 @@
+"""Fetch EUR/USD M1 bars from histdata.com (free, research use).
+
+Polite: one request per year, spaced; past years query month=None. Uses the
+maintained `histdata` package which handles histdata's anti-hotlink tk token.
+Output: data/raw/DAT_ASCII_EURUSD_M1_<year>.zip
+
+    YEARS=2019,2020,2021 python scripts/fetch_data.py
+"""
+import os
+import time
+
+from histdata import download_hist_data
+from histdata.api import Platform as P, TimeFrame as T
+
+YEARS = [y.strip() for y in os.environ.get("YEARS", "2019,2020,2021").split(",")]
+
+
+def main():
+    os.makedirs("data/raw", exist_ok=True)
+    for yr in YEARS:
+        f = download_hist_data(
+            year=yr, month=None, pair="eurusd",
+            platform=P.GENERIC_ASCII, time_frame=T.ONE_MINUTE,
+            output_directory="data/raw",
+        )
+        print("fetched", yr, "->", f)
+        time.sleep(2)  # be a good citizen
+
+
+if __name__ == "__main__":
+    main()