The gateway binary now has a real relay-facing configuration and QUIC control
handshake. It accepts a relay socket address, expected TLS server name, pinned
DER relay certificate, room code, LAN interface name, and advertised datagram
budget, then connects as role = gateway and waits for a welcome response.
The ALPN token moved into lanparty-ctrl so relay and gateway share the same
protocol identifier instead of carrying duplicate private constants. The gateway
still stops after the control-plane connection; AF_PACKET capture and injection
remain a later slice.
The connector test spins up a local Quinn server with a self-signed certificate,
trusts that certificate explicitly, verifies the outgoing gateway hello, and
checks the received welcome metadata.
Test Plan:
- cargo fmt --check
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
Refs: PLAN.md Linux gateway outbound relay connection
ddidderr
