fix: set sidebar to top and navigation to bottom in branding.desc

The QML files are designed for sidebar-at-top (logo, step name,
progress bar) and navigation-at-bottom (Back/Cancel/Next buttons
in a horizontal row). branding.desc had them reversed (sidebar
at bottom, navigation on right), causing the entire chrome to
render in the wrong positions — sidebar at bottom with inverted
shadow and progress bar, navigation as a vertical strip on the
right side.

Changed: sidebar: qml,top | navigation: qml,bottom

packages/calamares-branding-antergos-next/branding.desc

@@ -8,8 +8,8 @@ windowExpanding:    normal
 windowSize: 920px,630px
 windowPlacement: center
 
-sidebar: qml,bottom
-navigation: qml,right
+sidebar: qml,top
+navigation: qml,bottom
 
 strings:
     productName:         "Antergos NeXT"