Add fips-gateway binary to CI artifact and Docker build. Systemd
service unit with After=fips.service dependency and security
hardening. Debian and AUR package entries.
OpenWrt packaging: procd init script managing dnsmasq forwarding,
proxy NDP, RA route advertisements for the virtual IP pool, and a
global IPv6 prefix on br-lan to work around Android suppressing AAAA
queries on ULA-only networks. Sysctl config for IPv6 forwarding.
Gateway enabled by default in OpenWrt config. Ethernet transport
enabled by default.
Default gateway config section (commented out) in common fips.yaml.