Bootstrap used to end with `decnet updater --daemon` which forks and
detaches — invisible to systemctl, no auto-restart, dies on reboot.
Ships a decnet-updater.service template matching the pattern of the
other units (Restart=on-failure, log to /var/log/decnet/decnet.updater.log,
certs from /etc/decnet/updater, install tree at /opt/decnet), bundles
it alongside agent/forwarder/engine units, and the installer now
`systemctl enable --now`s it when --with-updater is set.
Rename log-file-path -> log-directory (maps to DECNET_LOG_DIRECTORY). Bundle
now ships three systemd units rendered with agent_name/master_host and installs
them into /etc/systemd/system/. Bootstrap replaces direct 'decnet X --daemon'
calls with systemctl enable --now. Each unit pins DECNET_SYSTEM_LOGS so agent,
forwarder, and deckies logs land at decnet.{agent,forwarder}.log and decnet.log
under /var/log/decnet.
