refactor(mqttx): convert from LXC to addon

MQTTX Web is a static browser-based MQTT client with no backend.
Makes more sense as an addon installable into any existing container
than as a dedicated LXC.

Addon installs into /opt/mqttx, builds web/ with yarn, serves via
Nginx on configurable port (default 8095). Supports install/update/uninstall.

install/mqttx-install.sh

@@ -1,49 +0,0 @@
-#!/usr/bin/env bash
-
-# Copyright (c) 2021-2026 community-scripts ORG
-# Author: MickLesk (CanbiZ)
-# License: MIT | https://github.com/community-scripts/ProxmoxVED/raw/main/LICENSE
-# Source: https://github.com/emqx/MQTTX
-
-source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
-color
-verb_ip6
-catch_errors
-setting_up_container
-network_check
-update_os
-
-msg_info "Installing Dependencies"
-$STD apt install -y \
-  nginx
-msg_ok "Installed Dependencies"
-
-NODE_VERSION="22" NODE_MODULE="yarn" setup_nodejs
-
-fetch_and_deploy_gh_release "mqttx" "emqx/MQTTX" "tarball" "latest" "/opt/mqttx"
-
-msg_info "Building MQTTX Web"
-cd /opt/mqttx/web
-$STD yarn install --frozen-lockfile
-$STD yarn build
-msg_ok "Built MQTTX Web"
-
-msg_info "Configuring Nginx"
-cat <<'EOF' >/etc/nginx/sites-available/default
-server {
-    listen 80;
-
-    root /opt/mqttx/web/dist;
-    index index.html;
-
-    location / {
-        try_files $uri $uri/ /index.html;
-    }
-}
-EOF
-systemctl restart nginx
-msg_ok "Configured Nginx"
-
-motd_ssh
-customize
-cleanup_lxc