Adds services/router.nix with systemd-networkd (eno1=WAN via DHCP,
eth0=LAN 10.0.0.1/24), nftables (NAT + firewall, default drop on WAN
in), dnsmasq (DHCP only — AdGuard Home keeps :53 for DNS), and sysctl
IP forwarding. NetworkManager is forced off on this host.
Port forwards live in ports.toml at the repo root and are imported via
builtins.fromTOML. Supports single ports, ranges ("26901-26902"), and
"both" protocol. Initial forwards: 22, 80, 443, 26900, 26901-26902.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
