feat(themes): declaratively manage icons, cursors, and dark/light modes

- Automatically detect light mode via 'light.mode' file in theme folder
- Read icon theme name from 'icons.theme' file in theme folder
- Switch Stylix polarity and iconTheme based on theme selection
- Add yaru-theme and bibata-cursors to default packages
- Remove obsolete imperative nomarchy-theme-set-gnome script

modules/home/default.nix

@@ -49,6 +49,8 @@ in
     mise
     jq
     xmlstarlet
+    yaru-theme
+    bibata-cursors
     nerd-fonts.jetbrains-mono
     nerd-fonts.roboto-mono
     nerd-fonts.fira-code