Daemon model

A two-tier daemon: the supervisor vmlabd (one per user) plus one lab daemon per running lab, auto-started by the CLI.

vmlab runs a two-tier daemon, auto-started by the CLI — there is no setup step.

Tier	Scope	Owns
Supervisor (vmlabd)	One per user, auto-started on first CLI use	Lab registry, global segments, cross-host peering, serialised template-store writes, host watchdogs, aggregated events
Lab daemon	One per running lab; spawned on up, reaped on down/destroy	QEMU processes, QMP/agent channels, the userspace network fabric, snapshots, the wscript runtime

If a lab daemon dies, the supervisor emits lab.daemon_crashed and marks the lab failed — there is no auto-restart (restart policy belongs to on handlers). Manual control: vmlab daemon start | stop | status.