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.
Mirrors the agent→forwarder pattern: `decnet swarmctl` now fires the
syslog-TLS listener as a detached Popen sibling so a single master
invocation brings the full receive pipeline online. --no-listener opts
out for operators who want to run the listener on a different host (or
under their own systemd unit).
Listener bind host / port come from DECNET_LISTENER_HOST and
DECNET_SWARM_SYSLOG_PORT — both seedable from /etc/decnet/decnet.ini.
PID at $(pid_dir)/listener.pid so operators can kill/restart manually.
decnet.ini.example ships alongside env.config.example as the
documented surface for the new role-scoped config. Mode, forwarder
targets, listener bind, and master ports all live there — no more
memorizing flag trees.
Extends tests/test_auto_spawn.py with two swarmctl cases: listener is
spawned with the expected argv + PID file, and --no-listener suppresses.
