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

themes/engine/scripts/nomarchy-theme-list

@@ -3,7 +3,7 @@ set -e
 
 {
   find ~/.config/nomarchy/themes/ -mindepth 1 -maxdepth 1 \( -type d -o -type l \) -printf '%f\n'
-  find "$NOMARCHY_PATH/assets/themes/" -mindepth 1 -maxdepth 1 -type d -printf '%f\n'
+  find "$NOMARCHY_PATH/themes/palettes/" -mindepth 1 -maxdepth 1 -type d -printf '%f\n'
 } | sort -u | while read -r name; do
   echo "$name" | sed -E 's/(^|-)([a-z])/\1\u\2/g; s/-/ /g'
 done