修复价格快照接口 NameError：补全 order_prices 初始化。

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

app.py

@@ -5802,6 +5802,7 @@ def api_price_snapshot():
             }
         )
 
+    order_prices = []
     for r in order_rows:
         margin = float(r["margin_capital"] or 0)
         leverage = float(r["leverage"] or 0)