Start adding Miniflux support plus other cleanup

- Modernize old async code
- Update to .NET 10
- Adjust namespace
- Bypass update check when debugging

Application/MainWindow/FeedCreation.cs

@@ -3,6 +3,7 @@ using System;
 using System.Linq;
 using System.Net;
 using System.Threading;
+using FeedCenter.Feeds;
 
 namespace FeedCenter;