fix(market): resolve price staleness issue in GetCurrentKlines

## Problem
GetCurrentKlines had two critical bugs causing price data to become stale:
1. Incorrect return logic: returned error even when data fetch succeeded
2. Race condition: returned slice reference instead of deep copy, causing concurrent data corruption

## Impact
- BTC price stuck at 106xxx while actual market price was 107xxx+
- LLM calculated take-profit based on stale prices → orders failed validation
- Statistics showed incorrect P&L (0.00%) due to corrupted historical data
- Alt-coins filtered out due to failed market data fetch

## Solution
1. Fixed return logic: only return error when actual failure occurs
2. Return deep copy instead of reference to prevent race conditions
3. Downgrade subscription errors to warnings (non-blocking)

## Test Results
✅ Price updates in real-time
✅ Take-profit orders execute successfully
✅ P&L calculations accurate
✅ Alt-coins now tradeable

Related: Price feed mechanism, concurrent data access

market/monitor.go

@@ -297,19 +297,32 @@ func (m *WSMonitor) GetCurrentKlines(symbol string, _time string) ([]Kline, erro
 		// 如果Ws数据未初始化完成时,单独使用api获取 - 兼容性代码 (防止在未初始化完成是,已经有交易员运行)
 		apiClient := NewAPIClient()
 		klines, err := apiClient.GetKlines(symbol, _time, 100)
-		m.getKlineDataMap(_time).Store(strings.ToUpper(symbol), klines) //动态缓存进缓存
+		if err != nil {
+			return nil, fmt.Errorf("获取%v分钟K线失败: %v", _time, err)
+		}
+
+		// 动态缓存进缓存
+		m.getKlineDataMap(_time).Store(strings.ToUpper(symbol), klines)
+
+		// 订阅 WebSocket 流
 		subStr := m.subscribeSymbol(symbol, _time)
 		subErr := m.combinedClient.subscribeStreams(subStr)
 		log.Printf("动态订阅流: %v", subStr)
 		if subErr != nil {
-			return nil, fmt.Errorf("动态订阅%v分钟K线失败: %v", _time, subErr)
+			log.Printf("警告: 动态订阅%v分钟K线失败: %v (使用API数据)", _time, subErr)
 		}
-		if err != nil {
-			return nil, fmt.Errorf("获取%v分钟K线失败: %v", _time, err)
-		}
-		return klines, fmt.Errorf("symbol不存在")
+
+		// ✅ FIX: 返回深拷贝而非引用
+		result := make([]Kline, len(klines))
+		copy(result, klines)
+		return result, nil
 	}
-	return value.([]Kline), nil
+
+	// ✅ FIX: 返回深拷贝而非引用，避免并发竞态条件
+	klines := value.([]Kline)
+	result := make([]Kline, len(klines))
+	copy(result, klines)
+	return result, nil
 }
 
 func (m *WSMonitor) Close() {