Add AcmeCertProvider with domain-based and IP-based modes using rustls-acme.
AcmeTlsAcceptor::bind_acme() and TlsAcceptor::bind_acme() provide ACME-integrated
TLS acceptance with automatic cert renewal via background tokio task.
Feature-gated behind 'acme' (implies 'tls'). Unit tests for config construction;
integration test for LE staging marked #[ignore].
Add iroh QUIC P2P transport using tokio::io::join for stream duplexing
per ADR-003. Default relay is n0's https://relay.iroh.network/ (ADR-009).
Proxy URL passed to Endpoint::builder (ADR-010). Integration test marked
#[ignore] for CI since it requires iroh relay connectivity.
