POST /api/v1/workers/{name}/start — 202 on acceptance, 404 unknown
worker, 503 if the unit file is not installed, 502 if systemctl
returns non-zero (stderr snippet in detail, full stack logged).
Admin only.
POST /api/v1/workers/start-all — best-effort: walks the worker list
in dependency order (bus → api → data-plane), skips already-active
and uninstalled units, aggregates outcomes into
{started, already_running, failed[]}. Returns 200 even on partial
failure; the caller reads the three lists.
Both endpoints delegate to the systemd_control helper, so the attack
surface for "what gets executed" is locked to `decnet-<validated-name>
.service` at two layers (router KNOWN_WORKERS + helper regex).