A vhost may be ident@host, not just host: apply_vhost splits it and sends
CHGIDENT for the ident plus CHGHOST for the host. valid_vhost validates
the optional ident part; ON/SET/ACTIVATE/identify all route through
apply_vhost, so a bare host still works unchanged. New SetIdent action.
REQUEST <host> records a pending vhost (typed Option<PendingVhost> on the
account, VhostRequested/VhostRequestCleared events); operators review with
WAITING and either ACTIVATE (assign + apply to online sessions) or REJECT
(clear it). Host validation and the operator gate are shared with SET.
New HostServ pseudo-service assigns and applies vhosts. A vhost is a typed
Option<Vhost>{host,setter,ts} on the account (VhostSet/VhostDeleted events),
applied to the displayed host on identify and re-applied by ON; OFF restores
the normal host for the session. Operators SET/DEL (applied at once to
online sessions) and LIST; hosts are validated as dot-separated labels.
New SetHost NetAction -> InspIRCd ENCAP <target-sid> CHGHOST <uid> <host>.
