Fixes backup system authentication and hostname resolution issues.
Changes:
- Change PermitRootLogin from "no" to "prohibit-password" in global SSH config
(allows key-based root login for host-to-host backups while blocking passwords)
- Update fuchsia onsite backup to use viridian.home.arpa FQDN instead of shortname
- Update SSH knownHosts to use FQDNs (fuchsia.home.arpa, viridian.home.arpa)
(system-level config uses FQDNs, user shortcuts remain in home-manager)
This enables the complete 3-2-1 backup strategy with automated backups working
correctly between fuchsia and viridian, and fuchsia to BorgBase.
Restructures SSH trust relationships from global to host-specific configuration
for better locality of concern and principle of least privilege.
Changes:
- Collapse nixos/common/global/ssh/ back to ssh.nix (single-file module)
- Move internal host trust (fuchsia/viridian) to per-host services/ssh/
- Split BorgBase known hosts by repository (li9kg944 for fuchsia, r7ag7x1w for viridian)
- Add viridian SSH server config to accept backup connections from fuchsia
- Add fuchsia borgbackup passphrase for offsite backups
- Configure viridian to create /srv/borg-repo/fuchsia for remote backups
This enables the 3-2-1 backup strategy with fuchsia backing up to both viridian
(onsite) and BorgBase (offsite) with proper SSH authentication.
