feat(tools): add root-password and update-server tools

- add `tools/root-password.sh` to change root password interactively or generate a random one
- add `tools/update-server.sh` to run apt update/upgrade/autoremove/autoclean
- register both tools in `lxs.sh` dispatcher and `tools/index.sh` interactive menu
- document new tools in README.md

lxs.sh

@@ -287,6 +287,8 @@ cmd_tool() {
         system)    download_and_run "tools/system-infos.sh" "$@" ;;
         benchmark) download_and_run "tools/server-benchmark.sh" "$@" ;;
         harden)    download_and_run "tools/harden.sh" "$@" ;;
+        root-password) download_and_run "tools/root-password.sh" "$@" ;;
+        update)    download_and_run "tools/update-server.sh" "$@" ;;
         "")        echo -e "${RED}[✗] Missing tool name. Try: lxs help${NC}"; return 1 ;;
         *)         echo -e "${RED}[✗] Unknown tool: $tool. Try: lxs help${NC}"; return 1 ;;
     esac