修复 scale-in 后 leg.EntryPrice 不更新 + 重启恢复时加载 scale prices

- trader.go: scale-in 后用 weightedAvgPrice 更新 LongLeg/ShortLeg.EntryPrice
- trader.go: restoreOpenPositions 从 orders 表加载 scale prices 重建完整价格切片
- db/trade_repo.go: 新增 GetScalePrices(tradeID) 方法
- README: v1.2.1 版本记录

db/trade_repo.go

@@ -235,6 +235,31 @@ func scanTrades(rows *sql.Rows) ([]TradeRecord, error) {
 	return trades, rows.Err()
 }
 
+// GetScalePrices returns scale-in order prices for a trade, grouped by leg.
+func (d *DB) GetScalePrices(tradeID int64) (longPrices, shortPrices []float64, err error) {
+	rows, err := d.Query(`SELECT leg, price FROM orders
+		WHERE trade_id=? AND type='scale' AND price IS NOT NULL
+		ORDER BY id`, tradeID)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var leg string
+		var price float64
+		if err := rows.Scan(&leg, &price); err != nil {
+			return nil, nil, err
+		}
+		switch leg {
+		case "long":
+			longPrices = append(longPrices, price)
+		case "short":
+			shortPrices = append(shortPrices, price)
+		}
+	}
+	return longPrices, shortPrices, rows.Err()
+}
+
 // GetClosedStats returns convergence counts from the database.
 func (d *DB) GetClosedStats() (converged, diverged, flat, total int, err error) {
 	if err = d.QueryRow("SELECT COUNT(*) FROM trades WHERE status='closed'").Scan(&total); err != nil {