fix: 请求收益曲线时自动回填历史数据

- GetNavHistoryAsync现在会自动检查是否有历史数据
- 无历史数据时自动调用BackfillNavHistoryInternalAsync
- 拆分内部回填方法，避免重复验证权限

AssetManager.Services/PortfolioNavService.cs

@@ -44,6 +44,17 @@ public class PortfolioNavService : IPortfolioNavService
         var endDate = request.endDate ?? DateTime.Today;
         var startDate = request.startDate ?? endDate.AddDays(-30);
 
+        // 检查是否有历史数据，没有则自动回填
+        var existingCount = await _db.Queryable<PortfolioNavHistory>()
+            .Where(n => n.PortfolioId == portfolioId)
+            .CountAsync();
+
+        if (existingCount == 0)
+        {
+            _logger.LogInformation("组合 {PortfolioId} 无净值历史数据，自动开始回填", portfolioId);
+            await BackfillNavHistoryInternalAsync(portfolioId, portfolio);
+        }
+
         // 查询净值历史
         var navHistory = await _db.Queryable<PortfolioNavHistory>()
             .Where(n => n.PortfolioId == portfolioId)
@@ -244,6 +255,14 @@ public class PortfolioNavService : IPortfolioNavService
             throw new Exception("Portfolio not found or access denied");
         }
 
+        return await BackfillNavHistoryInternalAsync(portfolioId, portfolio, force);
+    }
+
+    /// <summary>
+    /// 内部回填方法（已验证权限）
+    /// </summary>
+    private async Task<BackfillNavResponse> BackfillNavHistoryInternalAsync(string portfolioId, Portfolio portfolio, bool force = false)
+    {
         // 获取所有交易记录，按时间排序
         var transactions = await _db.Queryable<Transaction>()
             .Where(t => t.PortfolioId == portfolioId)
@@ -288,10 +307,6 @@ public class PortfolioNavService : IPortfolioNavService
         // 遍历每个交易日
         for (var date = startDate; date <= endDate; date = date.AddDays(1))
         {
-            // 跳过周末（可选，美股周末无交易）
-            // if (date.DayOfWeek == DayOfWeek.Saturday || date.DayOfWeek == DayOfWeek.Sunday)
-            //     continue;
-
             // 检查是否已存在该日期的净值记录（非强制模式）
             if (!force)
             {