Start adding Miniflux support plus other cleanup

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

Application/Options/CategoryWindow.xaml

@@ -9,7 +9,8 @@
         xmlns:controls="clr-namespace:ChrisKaczor.Wpf.Windows;assembly=ChrisKaczor.Wpf.Windows.ControlBox"
         xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
         xmlns:options="clr-namespace:FeedCenter.Options"
-        d:DataContext="{d:DesignInstance Type=feedCenter:Category}"
+        xmlns:feeds="clr-namespace:FeedCenter.Feeds"
+        d:DataContext="{d:DesignInstance Type=feeds:Category}"
         Title="CategoryWindow"
         Width="300"
         ResizeMode="NoResize"