decnet canary launches the HTTP + DNS callback receiver via
decnet.canary.worker.run. Mirrors the shape of decnet webhook
(typer command with --daemon flag, asyncio.run in the foreground).
Deliberately NOT added to MASTER_ONLY_COMMANDS — every host that
hosts deckies runs its own canary worker, and the bus events stay
local to that host (per-host webhook fanout handles SIEM egress).
