When email is configured and a REGISTER includes an address, the account
starts unverified and a confirmation code is emailed. CONFIRM <code>
verifies it (a federated AccountVerified event); INFO shows an unconfirmed
email until then. Emailed codes now carry a purpose (reset vs confirm).
Adds a config-driven mailer: a SendEmail action the link layer pipes to
a configured command (sendmail -t, msmtp, ...) off-thread. NickServ
RESETPASS <account> emails a short-lived code to the address on file;
RESETPASS <account> <code> <newpassword> completes the reset. Codes are
node-local; the password change itself federates.
