Close the lifecycle loop for the correlation graph: every decky now
enters the substrate with an explicit `trigger=creation` event
(old_services=[] ⇒ new_services=<initial>) and leaves it with
`trigger=retirement` (old=<current> ⇒ new=[]). With scheduled/operator
mutations already flowing through emit_decky_mutated, the entire decky
lifecycle is now a well-formed sequence of mutation events — the
correlator can fold substrate_state(t) at any T by replaying them.
Lazy-imports mutator.events to dodge the engine↔mutator circular
dependency. Bus is None at CLI sites; the syslog write is what the
correlator consumes. Emission is soft-failing so a broken log path
never aborts a deploy.