Add 'New Update' notification flow

Introduce a small update-notification feature: add AppEvents.HasUpdateNotified event and have TaskManager publish it when update messages exist. Add localized resource key (menuNewUpdate) and expose it in the ResUI designer; update resource files for several languages. In the UI, add a New Update button in MainWindow.xaml, wire its click to the existing check-update handler, bind its visibility to a new BlNewUpdate property on MainWindowViewModel, and subscribe the viewmodel to the new event. Also reset the notification flag after showing the Check Update dialog.

v2rayN/ServiceLib/Manager/TaskManager.cs

@@ -142,5 +142,10 @@ public class TaskManager
             await _updateFunc?.Invoke(false, msg);
         }
         NoticeManager.Instance.Enqueue(string.Join("\n", msgs));
+
+        if (msgs.Count > 0)
+        {
+            AppEvents.HasUpdateNotified.Publish(true);
+        }
     }
 }