Symlink ~lass/Maildir to vmail, add lass to virtualMail group,
install notmuch + muchsync for remote sync.

- notmuch: remove hardcoded mailboxes, use folder: queries instead of tags
- mutt: auto-discover sieve folders from Maildir at startup
- muchsync: connect to neoprism.lassul.us:45621 instead of green

- Remove declarative sieveScript, manage rules dynamically via ManageSieve (port 4190)
- Replace krebs.iptables with networking.firewall.allowedTCPPorts
- Add /var/sieve to borg backup paths

IMAPS, SMTP submission, sieve filtering, DKIM, full-text search.
Remove dead code internet-gateway.nix and hackerfleet exim router.
Add mail and DKIM dirs to borg backup.

Use `nix build --print-out-paths` + PYTHONPATH instead of `nix shell`
for the websocket-client bootstrap. Caches the store path in /tmp.
Goes from 30s+ to under 1s.