Replace legacy container/install scripts with a single tools/addon/cronmaster.sh addon. The new script consolidates install, update and uninstall flows, uses community-scripts core functions, fetches prebuilt GitHub releases, sets up Node.js (defaults to v22), creates a systemd service and an update helper (/usr/local/bin/update_cronmaster). Removed ct/cronmaster.sh and install/cronmaster-install.sh to avoid duplication and centralize maintenance.
