Fix LIVE SoT P0/P1: closing state machine, OO exchange fills, BN balances.

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

backend/app/strategy/open_capacity.py

@@ -70,8 +70,15 @@ def _live_balances() -> dict[str, float | None]:
 
         ex = str(load_runtime_settings().exchange or "").strip().lower()
         if ex in ("binance", "bn"):
-            # 币安资金接口尚未接入；返回 None 使可开判定为「未知」而非误用 OKX
-            logger.debug("open_capacity: binance live balance not wired; treating as unknown")
+            from ..live.binance_trade import BinanceTradeClient
+
+            client = BinanceTradeClient()
+            try:
+                bal = client.fetch_balances()
+                out["trading_usdt"] = _f(bal.get("trading_usdt"))
+                out["trading_usdc"] = _f(bal.get("trading_usdc"))
+            finally:
+                client.close()
         else:
             from ..live.okx_funds import OkxFundsClient