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

installer/install.sh

@@ -1274,6 +1274,11 @@ execute_installation() {
         info  "The system is installed; fix /etc/nixos before rebooting if possible."
     fi
 
+    # 9.10 Set ownership of /etc/nixos to the main user
+    info "Setting ownership of /etc/nixos for $USERNAME..."
+    nixos-enter --root /mnt -- chown -R "$USERNAME:users" /etc/nixos
+    success "Ownership updated"
+
     success "Installation complete!"
     rm -f "$STATE_FILE"
 }