Start adding Miniflux support plus other cleanup

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

Application/FeedErrorWindow.xaml.cs

@@ -5,6 +5,7 @@ using System.Windows;
 using System.Windows.Data;
 using System.Windows.Input;
 using ChrisKaczor.InstalledBrowsers;
+using FeedCenter.Feeds;
 using FeedCenter.Options;
 using FeedCenter.Properties;