feat: 用户访问时自动触发当日净值计算

修改 GetNavHistoryAsync：
- 检查是否存在今日净值记录
- 如果不存在，自动调用 CalculateAndSaveDailyNavAsync
- 捕获异常避免影响历史数据查询

收益：
- 用户每次访问收益曲线都能获取最新数据
- 无需手动触发或定时任务

AssetManager.Services/PortfolioNavService.cs

@@ -54,6 +54,27 @@ public class PortfolioNavService : IPortfolioNavService
             _logger.LogInformation("组合 {PortfolioId} 无净值历史数据，自动开始回填", portfolioId);
             await BackfillNavHistoryInternalAsync(portfolioId, portfolio);
         }
+        else
+        {
+            // 有历史数据，检查是否需要计算今日净值
+            var today = DateTime.Today;
+            var todayNavExists = await _db.Queryable<PortfolioNavHistory>()
+                .Where(n => n.PortfolioId == portfolioId && n.NavDate == today)
+                .AnyAsync();
+            
+            if (!todayNavExists)
+            {
+                _logger.LogInformation("组合 {PortfolioId} 今日净值不存在，自动计算", portfolioId);
+                try
+                {
+                    await CalculateAndSaveDailyNavAsync(portfolioId);
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogWarning(ex, "组合 {PortfolioId} 今日净值计算失败，将使用历史数据", portfolioId);
+                }
+            }
+        }
 
         // 查询净值历史
         var navHistory = await _db.Queryable<PortfolioNavHistory>()
@@ -77,45 +98,6 @@ 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
         {