POST /topologies/blank seeded the gateway decky with
archetype=host-gateway + network_mode=host, but neither was wired:
no compose writer reads network_mode and host-gateway is not a real
archetype. Replace with archetype=deaddeck + forwards_l3=true so the
gateway is a normal multi-homed bridge decky, consistent with how
compose.py interprets forwards_l3 (sysctl + NET_ADMIN).
Edge marked is_bridge=true, forwards_l3=true so downstream readers
(generator, compose, validator) see a real bridge attachment.
anti
cc9765e54e