Replace neomutt with vibe.mail.smtp.sendMail

Been meaning to do this for a while...

I forgot to set neomutt to use the config for it on my server and realised it was using sendmail for MTA rather than the gmail smtp and it dawned on me that vibe.mail.smtp.sendMail with a sendmail smtp server would be much cleaner than the dependency on neomutt and gmail-oauth2-tools. It also lets us simplify the validation code because we don't need to worry about the contents of the email being piped over bash (!)

Also included: transition pseudonym from Mio Iwakura to Neo Ar