feat(transport): real TLS-443 on the TCP backend (replaces HTTP/1.1 masquerade)

The TCP fallback now does a full outer TLS handshake (tokio-rustls 0.26 over
rustls 0.23, ring provider) before the Aura proto handshake, exactly like the
QUIC backend: on the wire it is indistinguishable from genuine HTTPS until the
inner Aura mutual-auth handshake starts. Removes v1's "light HTTP masquerade"
limitation; the real security boundary remains the inner PQ handshake.

- aura-transport::tcp: dropped the HTTP/1.1 preamble helpers and TcpOpts
  fields (masquerade, host, user_agent, server_header). New flow:
  TlsAcceptor::accept (server) / TlsConnector::connect (client) →
  tokio::io::split(TlsStream) → server_handshake / client_handshake → Session.
  Client reuses crate::quic::AcceptAnyServerCert (outer SNI not authenticated;
  inner handshake is the security boundary). Outer server cert auto-sourced
  from proto_cfg.server_cert_pem (no API change for the CLI's bind).
- ALPN default: ["h2", "http/1.1"] (DEFAULT_TCP_ALPN, exported).
- TcpOpts: now just { alpn: Option<Vec<Vec<u8>>> }.
- TcpClient::connect gains an outer-SNI &str param; DialConfig.sni passes it
  through (separate from the inner proto_cfg.server_name).
- tokio-rustls 0.26 added as a transport-local dependency (not workspace).

CLI updates: removed dead host/user_agent/server_header wiring; mask rotation
no longer touches TCP outer parameters (TLS doesn't have a Host header on
the wire). [transport] masquerade kept as a no-op for back-compat with old
configs (documented).

3 new tcp_loopback tests (default ALPN end-to-end, custom ALPN, outer SNI
mismatch still connects = proves accept-any is in effect). Workspace: 142
tests passed (+1), clippy -D warnings clean, fmt clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -282,6 +282,7 @@ dependencies = [
  "rustls-pki-types",
  "thiserror 1.0.69",
  "tokio",
+ "tokio-rustls",
  "tracing",
 ]
 
@@ -2659,6 +2660,16 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "tokio-rustls"
+version = "0.26.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1729aa945f29d91ba541258c8df89027d5792d85a8841fb65e8bf0f4ede4ef61"
+dependencies = [
+ "rustls",
+ "tokio",
+]
+
 [[package]]
 name = "tokio-util"
 version = "0.7.18"