User groups (!name) — a founder plus member accounts, each with group-
access flags (the shared flag primitive: F founder, f manage, i invite,
c chan-access, s set, m memo). REGISTER/DROP/INFO/LIST/ADD/DEL/FLAGS;
event-sourced and federated like accounts.
The flagship interconnection: a channel access entry may name a !group, so
every member inherits that channel access. Resolution is group-aware — a
new db.channel_caps() unions a user's direct access with any group they
belong to, and the engine's join handler auto-ops/voices through it. So
"ChanServ FLAGS #chan !team +o" auto-ops every member of !team, and
removing someone from the group revokes it. Opt-in.
