POST /topologies/{id}/lans previously called _auto_attach_gateway()
whenever a non-DMZ LAN was created, which wired the DMZ gateway decky
to every new subnet. That's why a deployed gateway ended up with
eth0..ethN on every LAN regardless of what the user drew in MazeNET.
Drop the auto-attach helper entirely. The DMZ_ORPHAN deploy-time
validator (decnet/topology/validate.py:65-110) stays strict — users
must explicitly wire the gateway to each subnet they want bridged,
which is the whole point of having a topology editor.
useMazeApi.ts: drop stale auto-bridge reference from comment.