Email owners before inactivity-expiry drops their account or channel

When [expire] warn_days is set and email is configured, the expiry sweep
now emails a heads-up to owners entering the warning window (inactive past
the threshold minus the lead time, but not yet expired) for whom an
address is on file — the founder's address for a channel. It's a chance to
keep the record by simply using it before the deadline.

Each idle spell warns at most once: a new AccountExpiryWarned /
ChannelExpiryWarned event marks the record, and the next activity stamp
clears the mark so a later idle spell warns afresh. The warning email is a
first-class api template (fedserv_api:📧:expiry_warning), alongside
the reset and confirm mails.

src/grpc.rs

@@ -166,7 +166,9 @@ fn to_wire(entry: &LogEntry) -> Option<ReplicationEvent> {
         | Event::AccountNoExpire { .. }
         | Event::ChannelNoExpire { .. }
         | Event::AkillAdded { .. }
-        | Event::AkillRemoved { .. } => return None,
+        | Event::AkillRemoved { .. }
+        | Event::AccountExpiryWarned { .. }
+        | Event::ChannelExpiryWarned { .. } => return None,
     };
     Some(ReplicationEvent { origin: entry.origin().to_string(), seq: entry.seq(), lamport: entry.lamport(), kind: Some(kind) })
 }
@@ -425,6 +427,7 @@ mod tests {
             vhost_request: None,
             last_seen: 111,
             noexpire: false,
+            expiry_warned: false,
         };
         let registered = LogEntry::for_test("A", 0, 1, Event::AccountRegistered(Box::new(acct)));
         let wire = to_wire(&registered).expect("account registration replicates");