fix: 修复收益曲线统计数据与组合详情不一致的问题

问题：
- 收益曲线接口 totalReturn 直接取净值历史最后一条的 cumulativeReturn
- 如果净值历史数据过时，统计信息会与当前持仓数据不一致

修复：
- 在 GetNavHistoryAsync 中检查净值历史最后一条是否为今天
- 如果不是，获取当前持仓数据实时计算累计收益率
- 更新 statistics.TotalReturn 为实时值

影响：
- 组合详情 historicalChange 和收益曲线 totalReturn 将保持一致

AssetManager.Services/PortfolioNavService.cs

@@ -77,6 +77,45 @@ public class PortfolioNavService : IPortfolioNavService
         // 计算统计指标
         var returns = navHistory.Select(n => (double)n.DailyReturn).Where(r => r != 0).ToList();
         var statistics = CalculateStatistics(returns, navHistory);
+        
+        // 如果净值历史的最后一条不是今天，实时计算当前累计收益率
+        var lastNavDate = navHistory.Last().NavDate;
+        if (lastNavDate < DateTime.Today)
+        {
+            // 获取当前持仓数据
+            var positions = await _db.Queryable<PortfolioPosition>()
+                .Where(p => p.PortfolioId == portfolioId)
+                .ToListAsync();
+            
+            if (positions.Any())
+            {
+                // 计算当前总市值和总成本
+                decimal totalValue = 0;
+                decimal totalCost = 0;
+                
+                foreach (var pos in positions)
+                {
+                    var currentValue = pos.Shares * pos.CurrentPrice;
+                    var cost = pos.Shares * pos.AverageCost;
+                    
+                    // 汇率转换
+                    var currentInTarget = await _exchangeRateService.ConvertAmountAsync(currentValue, pos.Currency, portfolio.Currency);
+                    var costInTarget = await _exchangeRateService.ConvertAmountAsync(cost, pos.Currency, portfolio.Currency);
+                    
+                    totalValue += currentInTarget;
+                    totalCost += costInTarget;
+                }
+                
+                // 计算实时累计收益率
+                if (totalCost > 0)
+                {
+                    var realTimeReturn = (double)((totalValue - totalCost) / totalCost * 100);
+                    statistics.TotalReturn = Math.Round(realTimeReturn, 2);
+                    _logger.LogDebug("实时计算累计收益率: {RealTimeReturn}%, 总市值: {TotalValue}, 总成本: {TotalCost}", 
+                        realTimeReturn, totalValue, totalCost);
+                }
+            }
+        }
 
         return new NavHistoryResponse
         {