Add GroupServ, with groups that grant channel access

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.

src/grpc.rs

@@ -176,6 +176,11 @@ fn to_wire(entry: &LogEntry) -> Option<ReplicationEvent> {
         | Event::ReportFiled { .. }
         | Event::ReportClosed { .. }
         | Event::ReportDeleted { .. }
+        | Event::GroupRegistered { .. }
+        | Event::GroupDropped { .. }
+        | Event::GroupFounderSet { .. }
+        | Event::GroupFlagsSet { .. }
+        | Event::GroupMemberDel { .. }
         | Event::OperGranted { .. }
         | Event::OperRevoked { .. }
         | Event::SessionExceptionAdded { .. }