feat(host-backup): custom SSH port for Borg remote targets
Add Borg destinations no longer assume port 22. The Monitor form and
the shell TUI both take an optional port (default 22, range 1-65535)
and embed it in the persisted ssh://user@host:port/path URL. BORG_RSH,
the sshpass key installer and the capacity probe all honour it.
Reported by @songochain in #236 — NAS-style Borg hosts on non-standard
SSH ports are now first-class targets.
Existing borg-targets.txt entries without a port keep working; the
port is only serialised into the URL when it differs from 22.
MacRimi
91b4200179