fix: 添加 /api/v1/portfolio/assets 端点

- IPortfolioFacade 添加 GetTotalAssetsAsync 方法
- PortfolioFacade 实现 GetTotalAssetsAsync
- PortfolioController 添加 [HttpGet("assets")] 端点（放在 {id} 路由之前）

AssetManager.API/Controllers/PortfolioController.cs

@@ -78,6 +78,23 @@ public class PortfolioController : ControllerBase
         });
     }
 
+    /// <summary>
+    /// 获取用户总资产
+    /// </summary>
+    [HttpGet("assets")]
+    public async Task<ActionResult<ApiResponse<TotalAssetsResponse>>> GetTotalAssets()
+    {
+        var userId = GetCurrentUserId();
+        var totalAssets = await _portfolioFacade.GetTotalAssetsAsync(userId);
+        
+        return Ok(new ApiResponse<TotalAssetsResponse>
+        {
+            code = Models.StatusCodes.Success,
+            data = totalAssets,
+            message = "success"
+        });
+    }
+
     /// <summary>
     /// 获取投资组合详情
     /// </summary>

AssetManager.Services/IPortfolioFacade.cs

@@ -56,4 +56,9 @@ public interface IPortfolioFacade
     /// 回填净值历史
     /// </summary>
     Task<BackfillNavResponse> BackfillNavHistoryAsync(string portfolioId, string userId, bool force = false);
+    
+    /// <summary>
+    /// 获取用户总资产
+    /// </summary>
+    Task<TotalAssetsResponse> GetTotalAssetsAsync(string userId);
 }

AssetManager.Services/PortfolioFacade.cs

@@ -186,4 +186,13 @@ public class PortfolioFacade : IPortfolioFacade
         
         return await _navService.BackfillNavHistoryAsync(portfolioId, userId, force);
     }
+
+    /// <summary>
+    /// 获取用户总资产
+    /// </summary>
+    public async Task<TotalAssetsResponse> GetTotalAssetsAsync(string userId)
+    {
+        _logger.LogInformation("获取用户总资产: {UserId}", userId);
+        return await _portfolioService.GetTotalAssetsAsync(userId);
+    }
 }