Add lazy inactivity-expiry for accounts and channels

Accounts and channels now carry a last-activity stamp and are dropped
once inactive past a configured threshold. A login stamps the account, a
join stamps the channel — both coalesced to at most one log entry per day
so routine traffic doesn't bloat the log, and stamps replicate so
activity on any node keeps a record alive network-wide.

Expiry is lazy in the proven style: a periodic pass computes it from the
stored stamps with no per-record timer, reusing the same relation the
vhost and suspension expiries use. The sweep spares operator accounts,
accounts with a live session, occupied channels, and anything an operator
has pinned with the new NOEXPIRE command (NickServ NOEXPIRE <account>,
ChanServ NOEXPIRE <#channel>, both Priv::Admin). Each expiry is announced
to the audit channel and clears the channel's +r.

Configured under [expire] (accounts_days / channels_days); a zero or
omitted field leaves that kind never expiring, and omitting the section
disables expiry entirely.

src/grpc.rs

@@ -160,7 +160,11 @@ fn to_wire(entry: &LogEntry) -> Option<ReplicationEvent> {
         | Event::VhostOfferRemoved { .. }
         | Event::VhostForbidAdded { .. }
         | Event::VhostForbidRemoved { .. }
-        | Event::VhostTemplateSet { .. } => return None,
+        | Event::VhostTemplateSet { .. }
+        | Event::AccountSeen { .. }
+        | Event::ChannelUsed { .. }
+        | Event::AccountNoExpire { .. }
+        | Event::ChannelNoExpire { .. } => return None,
     };
     Some(ReplicationEvent { origin: entry.origin().to_string(), seq: entry.seq(), lamport: entry.lamport(), kind: Some(kind) })
 }
@@ -417,6 +421,8 @@ mod tests {
             greet: String::new(),
             vhost: None,
             vhost_request: None,
+            last_seen: 111,
+            noexpire: false,
         };
         let registered = LogEntry::for_test("A", 0, 1, Event::AccountRegistered(Box::new(acct)));
         let wire = to_wire(&registered).expect("account registration replicates");