fix: FRED fetch — add browser User-Agent + print diagnostics to stdout

FRED blocks requests without a valid User-Agent. Added headers matching
a real browser. Also added print() calls so fetch errors appear in
docker logs (logger.warning goes to system_logs table, not stdout).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/fred_bootstrap.py

@@ -159,10 +159,24 @@ CATEGORIES = sorted({v["category"] for v in FRED_SERIES.values()})
 _FRED_CSV_URL = "https://fred.stlouisfed.org/graph/fredgraph.csv?id={series_id}"
 
 
+_HEADERS = {
+    "User-Agent": (
+        "Mozilla/5.0 (Windows NT 10.0; Win64; x64) "
+        "AppleWebKit/537.36 (KHTML, like Gecko) "
+        "Chrome/124.0.0.0 Safari/537.36"
+    ),
+    "Accept": "text/csv,text/plain,*/*",
+    "Accept-Language": "en-US,en;q=0.9",
+}
+
+
 def _fetch_fred_csv(series_id: str, from_date: str) -> Optional[pd.DataFrame]:
     url = _FRED_CSV_URL.format(series_id=series_id)
+    print(f"[FRED] Fetching {series_id} from {url}", flush=True)
     try:
-        resp = httpx.get(url, timeout=30, follow_redirects=True)
+        with httpx.Client(timeout=httpx.Timeout(10.0, connect=10.0), follow_redirects=True) as client:
+            resp = client.get(url, headers=_HEADERS)
+        print(f"[FRED] {series_id} status={resp.status_code} len={len(resp.content)}", flush=True)
         resp.raise_for_status()
         from io import StringIO
         df = pd.read_csv(StringIO(resp.text), parse_dates=["DATE"], index_col="DATE")
@@ -170,8 +184,10 @@ def _fetch_fred_csv(series_id: str, from_date: str) -> Optional[pd.DataFrame]:
         df["value"] = pd.to_numeric(df["value"], errors="coerce")
         df = df.dropna()
         df = df[df.index >= pd.Timestamp(from_date)]
+        print(f"[FRED] {series_id}: {len(df)} rows from {from_date}", flush=True)
         return df.sort_index()
     except Exception as e:
+        print(f"[FRED] ERROR {series_id}: {type(e).__name__}: {e}", flush=True)
         logger.warning(f"[FRED] Failed to fetch {series_id}: {e}")
         return None