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-snapshot

@@ -3,7 +3,6 @@
 set -e
 
 COMMAND="$1"
-NOMARCHY_PATH=${NOMARCHY_PATH:-$HOME/.local/share/nomarchy}
 
 if [[ -z $COMMAND ]]; then
   echo "Usage: nomarchy-snapshot <create|restore>" >&2