feat: add Etherpad

Adds a new LXC helper-script for Etherpad (https://etherpad.org), a
real-time collaborative document editor (Node.js / pnpm).

- ct/etherpad.sh — launcher + update_script using check_for_gh_release
  against ether/etherpad-lite.
- install/etherpad-install.sh — Node.js 22 via NodeSource, pnpm via
  corepack, clone latest release tag, pnpm install --frozen-lockfile &&
  pnpm run build:etherpad, dedicated etherpad system user, systemd unit
  running `pnpm run prod`.
- json/etherpad.json — category 12 (Documents & Notes), port 9001,
  default credentials none, default resources 2 vCPU / 2 GB RAM / 8 GB
  disk on Debian 12 unprivileged.

Refs ether/etherpad#7529

install/etherpad-install.sh

@@ -0,0 +1,89 @@
+#!/usr/bin/env bash
+
+# Copyright (c) 2021-2026 community-scripts ORG
+# Author: John McLear (JohnMcLear)
+# License: MIT | https://github.com/community-scripts/ProxmoxVED/raw/main/LICENSE
+# Source: https://etherpad.org
+
+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 \
+  git \
+  curl \
+  ca-certificates \
+  build-essential \
+  pkg-config \
+  libsqlite3-dev
+msg_ok "Installed Dependencies"
+
+NODE_VERSION="22" setup_nodejs
+
+msg_info "Enabling pnpm via corepack"
+export COREPACK_ENABLE_DOWNLOAD_PROMPT=0
+$STD corepack enable
+msg_ok "Enabled pnpm"
+
+msg_info "Creating etherpad User"
+if ! id -u etherpad >/dev/null 2>&1; then
+  useradd --system --create-home --home-dir /var/lib/etherpad --shell /usr/sbin/nologin etherpad
+fi
+msg_ok "Created etherpad User"
+
+msg_info "Cloning Etherpad"
+LATEST_TAG=$(curl -fsSL https://api.github.com/repos/ether/etherpad-lite/releases/latest | grep -oP '"tag_name":\s*"\K[^"]+')
+if [ -z "${LATEST_TAG}" ]; then
+  msg_error "Unable to determine latest Etherpad release"
+  exit 1
+fi
+$STD git clone --depth 1 --branch "${LATEST_TAG}" https://github.com/ether/etherpad-lite.git /opt/etherpad-lite
+echo "${LATEST_TAG}" >/opt/etherpad-lite/.version
+msg_ok "Cloned Etherpad ${LATEST_TAG}"
+
+msg_info "Building Etherpad"
+cd /opt/etherpad-lite
+$STD pnpm install --frozen-lockfile
+$STD pnpm run build:etherpad
+msg_ok "Built Etherpad"
+
+msg_info "Configuring Etherpad"
+cp /opt/etherpad-lite/settings.json.template /opt/etherpad-lite/settings.json
+sed -i 's#"ip": *"127.0.0.1"#"ip": "0.0.0.0"#' /opt/etherpad-lite/settings.json
+chown -R etherpad:etherpad /opt/etherpad-lite
+msg_ok "Configured Etherpad"
+
+msg_info "Creating Service"
+cat <<EOF >/etc/systemd/system/etherpad.service
+[Unit]
+Description=Etherpad Collaborative Editor
+Documentation=https://etherpad.org/doc
+After=network.target
+
+[Service]
+Type=simple
+User=etherpad
+Group=etherpad
+WorkingDirectory=/opt/etherpad-lite
+Environment=NODE_ENV=production
+ExecStart=/usr/bin/env pnpm run prod
+Restart=always
+RestartSec=5
+LimitNOFILE=65536
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=multi-user.target
+EOF
+systemctl enable -q --now etherpad
+msg_ok "Created Service"
+
+motd_ssh
+customize
+cleanup_lxc