fix: use FRED official JSON API (bypasses CloudFlare) + API key UI

- fred_bootstrap.py: switch from CSV graph endpoint (CloudFlare-blocked)
  to api.stlouisfed.org/fred/series/observations JSON API; reads key
  from DB config 'fred_api_key'; returns clear error if key missing
- eco.py: add GET/POST /api/eco/fred-key to check/save the FRED API key
- CalendarPage.tsx: BootstrapPanel shows API key section with status,
  input to paste key + save button, disables Launch if key missing

Free key: fred.stlouisfed.org -> My Account -> API Keys

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

backend/routers/eco.py

@@ -48,6 +48,28 @@ def _run_bootstrap(from_date: str, series_ids: Optional[List[str]], force: bool)
         _bootstrap_status["running"] = False
 
 
+@router.get("/fred-key")
+def get_fred_key() -> Dict[str, Any]:
+    """Check if a FRED API key is configured."""
+    from services.database import get_config
+    key = get_config("fred_api_key") or ""
+    return {
+        "configured": bool(key),
+        "preview": (key[:6] + "…" + key[-4:]) if len(key) > 10 else ("***" if key else ""),
+    }
+
+
+@router.post("/fred-key")
+def save_fred_key(key: str = Query(..., description="FRED API key")) -> Dict[str, Any]:
+    """Save FRED API key to DB config."""
+    from services.database import set_config
+    key = key.strip()
+    if not key:
+        raise HTTPException(400, "Empty key")
+    set_config("fred_api_key", key)
+    return {"status": "saved", "preview": key[:6] + "…" + key[-4:]}
+
+
 @router.post("/bootstrap")
 def bootstrap(
     background_tasks: BackgroundTasks,