Formalises three ad-hoc publish paths that already existed:
automation-events.ts, metrics/automation-bridge.ts and the
hostSessionStatus singleton, now the host.session.status topic.
Both invariants the old code relied on are preserved. Publishing stays
fire-and-forget, so a failing subscriber cannot disturb a metrics poll or
a host delete. The automations engine subscribes to the bus at scheduler
start instead of being imported ad hoc, which keeps the edge
one-directional: automations may import repositories, hosts modules must
not import automations.