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.
New decnet/config_ini.py parses a role-scoped INI file via stdlib
configparser and seeds os.environ via setdefault — real env vars still
win, keeping full back-compat with .env.local flows.
[decnet] holds role-agnostic keys (mode, disallow-master, log-file-path);
the role section matching `mode` is loaded, the other is ignored
silently so a worker never reads master-only keys (and vice versa).
Loader is standalone in this commit — not wired into cli.py yet.
