Start adding Miniflux support plus other cleanup

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

Application/Options/CheckedFeedListItem.cs

@@ -1,6 +1,3 @@
-namespace FeedCenter.Options
-{
-    public class CheckedFeedListItem : CheckedListItem<Feed>
-    {
-    }
-}
+namespace FeedCenter.Options;
+
+public class CheckedFeedListItem : CheckedListItem<Feeds.Feed>;