Fix Runtime by adding TotalRuntimeInSeconds

src/Managing.Api/Models/Responses/UserStrategyDetailsViewModel.cs

@@ -33,9 +33,14 @@ namespace Managing.Api.Models.Responses
         public decimal ROIPercentage { get; set; }
 
         /// <summary>
-        /// Date and time when the strategy was started
+        /// Date and time when the strategy was started (only present when running, for live ticker)
         /// </summary>
-        public DateTime Runtime { get; set; }
+        public DateTime? Runtime { get; set; }
+
+        /// <summary>
+        /// Total accumulated runtime in seconds (including current session if running)
+        /// </summary>
+        public long TotalRuntimeSeconds { get; set; }
 
         /// <summary>
         /// Average percentage of successful trades