feat(tools): add welcome message (MOTD) management tool

- add `tools/welcome-message.sh` with view, set, and reset actions
- register `lxs tool welcome|motd` command in `lxs.sh`
- add option 7 to interactive tools menu in `tools/index.sh`
- document `lxs tool welcome` in README

tools/index.sh

@@ -63,9 +63,10 @@ menu_tools() {
         echo -e "  ${GREEN}[4]${NC} Change Root Password"
         echo -e "  ${CYAN}[5]${NC} Update Server"
         echo -e "  ${YELLOW}[6]${NC} Root SSH Password Login"
+        echo -e "  ${PURPLE}[7]${NC} Welcome Message (MOTD)"
         echo -e "  ${RED}[0]${NC} Back"
         echo ""
-        echo -e -n "${BOLD}Choice [0-6]: ${NC}"
+        echo -e -n "${BOLD}Choice [0-7]: ${NC}"
         read -r choice
 
         case $choice in
@@ -75,8 +76,9 @@ menu_tools() {
             4) run_sibling "tools/root-password.sh" ;;
             5) run_sibling "tools/update-server.sh" ;;
             6) run_sibling "tools/root-ssh-login.sh" ;;
+            7) run_sibling "tools/welcome-message.sh" ;;
             0) return ;;
-            *) echo -e "${RED}[✗] Invalid option. Please select 0-6.${NC}"; sleep 1; continue ;;
+            *) echo -e "${RED}[✗] Invalid option. Please select 0-7.${NC}"; sleep 1; continue ;;
         esac
 
         if [ "$choice" != "0" ]; then