iroh's Endpoint natively supports ALPN negotiation and set_alpns(). Our
HandlerRegistry dispatches exactly like iroh's own ProtocolMap/Router
pattern, but shared across both quinn and iroh connection sources. We
use iroh::Endpoint directly (not iroh::Router) because our HandlerRegistry
and AuthContext are shared across sources.
Correct the conflation of quinn/TLS/iroh as interchangeable transports.
They are complementary connectivity modes serving different deployment
contexts: quinn (public IP + TLS), iroh (NAT traversal via relay), TCP
(handler-specific, not core). Clarify that TLS cert = network identity,
not auth identity. Map stealth mode to HTTP handler on standard ALPNs
instead of byte-peeking. Resolve OQ-05 as one-way door. SendStream/
RecvStream now use internal enum dispatch for both quinn and iroh
streams.