Fix Firefox display access when configure.sh runs via su

Pass DISPLAY and WAYLAND_DISPLAY explicitly through the su call in
install.sh so Firefox can connect to the user's display session.
Remove the now-unnecessary DISPLAY=:0 fallback from get_nc_token.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

system_setup/install.sh

@@ -490,7 +490,7 @@ read -r -p "Run configure.sh now to set up your environment? [y/N]: " RUN_CONF
 if [[ "${RUN_CONF,,}" == "y" ]]; then
     if [[ -n "$SUDO_USER" ]]; then
         info "Running configure.sh as user '$SUDO_USER'..."
-        su - "$SUDO_USER" -c "bash '$CONF_SCRIPT'"
+        su - "$SUDO_USER" -c "DISPLAY='${DISPLAY}' WAYLAND_DISPLAY='${WAYLAND_DISPLAY}' bash '$CONF_SCRIPT'"
     else
         echo
         echo "configure.sh must be run as a non-root user. Please run:"