feat: 导航开关与 CTP 柜台手续费

系统设置可开关五类导航；手续费默认从 CTP 查询同步，本地/AKShare 作离线兜底；补充 FEES.md。

Co-authored-by: Cursor <cursoragent@cursor.com>

fee_sync.py

@@ -53,6 +53,7 @@ def _parse_akshare_row(row: dict, multiplier: float) -> Optional[dict]:
         "close_yesterday_ratio": round(close_y_ratio * multiplier, 8),
         "close_today_fixed": round(close_t_fixed * multiplier, 6),
         "close_today_ratio": round(close_t_ratio * multiplier, 8),
+        "source": "akshare",
     }