nickserv: AJOIN auto-join list

Adds the account auto-join list (AJOIN ADD/DEL/LIST): NickServ SVSJOINs you
into your listed channels each time you identify. The list is a typed
Vec<AjoinEntry> on the account, folded through the event log like the cert and
akick lists (persists and replays; no separate store), reached by modules
through the Store trait. New ForceJoin action serialises to InspIRCd SVSJOIN.
Shown in INFO. Operates on the caller's own account; the oper form for other
users waits on a privilege system.

nickserv/src/info.rs

@@ -17,5 +17,9 @@ pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db:
             Some(email) => ctx.notice(me, from.uid, format!("  Email      : {email} (unconfirmed)")),
             None => ctx.notice(me, from.uid, "  Email      : (none set)"),
         }
+        let ajoin = db.ajoin_list(&acct.name);
+        if !ajoin.is_empty() {
+            ctx.notice(me, from.uid, format!("  Auto-join  : {} channel(s) — see \x02AJOIN LIST\x02", ajoin.len()));
+        }
     }
 }