fix(distro): fix /etc/nixos ownership, theme discovery, and CLI wrappers

- installer: set recursive ownership of /etc/nixos to main user post-install
- themes: fix NOMARCHY_PATH and discovery logic for Lua theme menu
- scripts: update CLI wrappers (font, theme, wallpaper) to use Walker menus
- core: remove obsolete NOMARCHY_PATH and cleanup dead code
- features: add pkgs.lua for Walker and remove obsolete switcher.nix
- docs: update ROADMAP.md, SCRIPTS.md and STRUCTURE.md

features/scripts/utils/nomarchy-theme

@@ -15,6 +15,6 @@ case "$COMMAND" in
         nomarchy-theme-list
         ;;
     selector|*)
-        nomarchy-theme-selector
+        nomarchy-launch-walker -m menus:nomarchythemes --width 800 --minheight 400
         ;;
 esac