The setup except path closes the database; the coordinator created
above it now shuts down first so no listener can fire against the
closed connection. Regression test included.
One refresh pass builds the whole entity snapshot: active children,
today's instances with derived open/done/missed states, per-child
presence via the PresenceEngine (records converted to model objects),
rollup counts, and the custody cycle day. Interval configurable via
the new update_interval option, default five minutes.