nixos-infect emitted defaultGateway6.address="" and ipv6.routes=[{address="";
prefixLength=128}] for this v4-only Hetzner instance, so network-addresses-eth0.service
failed at boot ("ip route add /128 ... any valid prefix is expected rather than /128").
The box has no real IPv6 (link-local only, kernel-managed), so remove the empty IPv6
gateway, address, and route. IPv4 unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Port from terraform-hetzner branch. Adds the Hetzner cc-ci flake host with
all 3 root authorized keys so nixos-rebuild doesn't lock out SSH access.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
