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.