The relay now accepts WebTransport sessions on the same UDP socket that
serves raw QUIC. The ALPN-multiplexing QUIC listener owns the socket and
dispatches incoming connections: "nb-quic" continues to the existing
relay handler, "h3" is handed to webtransport-go via http3.Server.
Browsers reach the relay over 443/udp without a second port.
Client side:
- Native builds keep using raw QUIC (no WT dialer registered).
- WASM/browser builds gain a WebTransport dialer that bridges syscall/js
to the browser's WebTransport API and uses datagrams (matching the
native QUIC dialer's semantics — no head-of-line blocking).
- The race dialer learned a transport hint so clients skip dialers a
given relay has not advertised.
Management protocol carries the hint as a new RelayEndpoint{url,
transports[]} list on RelayConfig, mirroring how peers and proxies
announce capabilities. Older management servers that only send urls keep
working unchanged.
devcert build: relay generates an ECDSA P-256 cert with 13-day validity
(within the WebTransport serverCertificateHashes 14-day cap) and exposes
its SHA-256 so the WASM dialer can pin it.
Bumps quic-go v0.55.0 -> v0.59.0 (no API breaks for relay's importers)
and adds github.com/quic-go/webtransport-go v0.10.0.
