feat: add exchange_id field to trader_positions table

- Add exchange_id column to track which exchange the position is from
- Update all SELECT/INSERT queries to include exchange_id
- Set exchange_id when creating position record in AutoTrader
- Add migration to add column to existing tables

trader/auto_trader.go

@@ -1548,6 +1548,7 @@ func (at *AutoTrader) recordPositionChange(orderID, symbol, side, action string,
 		// 开仓：创建新的仓位记录
 		pos := &store.TraderPosition{
 			TraderID:     at.id,
+			ExchangeID:   at.exchange, // 记录具体的交易所ID
 			Symbol:       symbol,
 			Side:         side, // LONG or SHORT
 			Quantity:     quantity,