feat: FXStreet calendar — free upcoming events with forecasts (no API key)

FXStreet calendar.fxstreet.com/eventdate/ returns ~300-400 events over
6 weeks including consensus forecasts, no authentication required.
FF HTML scraper is blocked by Cloudflare even on residential IPs.
FMP free plan returns 403 on /economic_calendar (requires Starter plan).

- Add backend/services/fxstreet_calendar.py: single GET request returning
  all major currencies; maps Volatility 0/1/2 → low/medium/high
- Add POST /api/eco/fxs-sync + GET /api/eco/fxs-sync/status endpoints
- Add FXStreet to daily background sync in main.py (runs every 24h)
- Add "Sync Upcoming (FXStreet)" button in ImportPanel (no key needed)
- Fix FMP 403 error message to say endpoint requires Starter plan
- Keep FMP panel for users who upgrade to FMP Starter ($14.99/month)

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

backend/routers/eco.py

@@ -293,10 +293,11 @@ def upcoming_events() -> List[Dict[str, Any]]:
 
 # ── Forex Factory calendar ────────────────────────────────────────────────────
 
-_ff_import_status: Dict[str, Any] = {"running": False, "last_result": None}
-_ff_sync_status:   Dict[str, Any] = {"running": False, "last_result": None}
-_ff_scrape_status: Dict[str, Any] = {"running": False, "last_result": None}
-_te_sync_status:   Dict[str, Any] = {"running": False, "last_result": None}
+_ff_import_status:  Dict[str, Any] = {"running": False, "last_result": None}
+_ff_sync_status:    Dict[str, Any] = {"running": False, "last_result": None}
+_ff_scrape_status:  Dict[str, Any] = {"running": False, "last_result": None}
+_te_sync_status:    Dict[str, Any] = {"running": False, "last_result": None}
+_fxs_sync_status:   Dict[str, Any] = {"running": False, "last_result": None}
 
 # CSV search order: Docker image (/app), uploaded to /tmp, local dev paths
 _FF_CSV_CANDIDATES = [
@@ -469,6 +470,39 @@ def fmp_sync_status_ep() -> Dict[str, Any]:
     return _te_sync_status
 
 
+# ── FXStreet calendar (no API key required) ───────────────────────────────────
+
+def _run_fxs_sync(weeks_ahead: int):
+    global _fxs_sync_status
+    _fxs_sync_status["running"] = True
+    try:
+        from services.fxstreet_calendar import fetch_upcoming
+        result = fetch_upcoming(weeks_ahead=weeks_ahead)
+        _fxs_sync_status["last_result"] = result
+    except Exception as e:
+        logger.error(f"[eco/fxs-sync] Failed: {e}")
+        _fxs_sync_status["last_result"] = {"error": str(e)}
+    finally:
+        _fxs_sync_status["running"] = False
+
+
+@router.post("/fxs-sync")
+def fxs_sync(
+    background_tasks: BackgroundTasks,
+    weeks: int = Query(6, ge=1, le=12),
+) -> Dict[str, Any]:
+    """Fetch upcoming events + forecasts from FXStreet (no API key needed)."""
+    if _fxs_sync_status["running"]:
+        raise HTTPException(409, "FXStreet sync already running")
+    background_tasks.add_task(_run_fxs_sync, weeks)
+    return {"status": "started", "weeks_ahead": weeks}
+
+
+@router.get("/fxs-sync/status")
+def fxs_sync_status_ep() -> Dict[str, Any]:
+    return _fxs_sync_status
+
+
 @router.get("/calendar")
 def ff_calendar(
     period:     str            = Query("recent", description="recent|today|tomorrow|yesterday|this_week|next_week|previous_week|this_month|next_month|previous_month|custom"),