Fix bos-settings compile errors and use REGISTRY_TOKEN for publishing

bos-settings was scaffolded but never compiled. Fixes:
- main.rs: import gtk4::prelude (connect_activate/run)
- window.rs: disambiguate WidgetExt::display(); drop unused GBox import
- hyprland.rs: Label has no set_monospace -> use the monospace CSS class
- theme.rs: drop unused prelude import

Also switch package.yml to secrets.REGISTRY_TOKEN (scoped write:package),
since the auto Actions token is not authorized for the owner registry.

bos-settings/src/theme.rs

@@ -1,4 +1,3 @@
-use gtk4::prelude::*;
 use gtk4::CssProvider;
 
 const CSS: &str = r#"