Add TCP transport implementation and test harness support

Implement TCP transport for FIPS enabling firewall traversal and serving
as the foundation for future Tor transport. This is the first
connection-oriented transport in the system.

Key design decisions:
- FMP header-based framing: reuses existing 4-byte FMP common prefix for
  packet boundary recovery with zero framing overhead
- Session survives TCP reconnection: Noise/MMP/FSP state bound to npub,
  not TCP connection; MMP liveness is sole authority for peer death
- Connect-on-send: fresh connection on first send, transparent reconnect
- close_connection() trait method for cross-connection deduplication cleanup

New transport files:
- src/transport/tcp/mod.rs: TcpTransport, connection pool, accept loop
- src/transport/tcp/stream.rs: FMP-aware stream reader (shared with Tor)

Modified: transport trait (close_connection), TcpConfig, TransportHandle
match arms, create_transports(), initiate_connection() for connection-
oriented links, cross-connection tie-breaker cleanup, design docs.

Tree announce loop and TCP stability fixes:
- Preserve tree announce rate-limit state across reconnection: carry
  forward last_tree_announce_sent_ms when a peer reconnects so the
  rate-limit window isn't reset to zero
- Drop oversize TCP packets at sender: pre-send MTU check returns
  MtuExceeded instead of writing to the stream, preventing receiver-side
  connection teardown and reset-reconnect cycles

Chaos harness:
- TCP transport support: tcp_edges/has_tcp/tcp_peers in SimTopology,
  transport-aware config_gen with per-edge transport type, TCP port 443,
  pure-TCP node support
- Include all non-Ethernet edges in directed_outbound()
- Fix netem/links log messages to say "IP-based" instead of "UDP"
- Add tcp-chain, tcp-only, and tcp-mesh scenario files

Static harness:
- Transport-aware config generation (get_default_transport, transport_port)
- TCP transport injection via Python post-processing
- Add tcp-chain topology and docker-compose profile

src/node/mod.rs

@@ -28,6 +28,7 @@ use crate::transport::{
     Link, LinkId, PacketRx, PacketTx, TransportAddr, TransportError, TransportHandle, TransportId,
 };
 use crate::transport::udp::UdpTransport;
+use crate::transport::tcp::TcpTransport;
 #[cfg(target_os = "linux")]
 use crate::transport::ethernet::EthernetTransport;
 use crate::tree::TreeState;
@@ -598,6 +599,21 @@ impl Node {
             }
         }
 
+        // Create TCP transport instances
+        let tcp_instances: Vec<_> = self
+            .config
+            .transports
+            .tcp
+            .iter()
+            .map(|(name, config)| (name.map(|s| s.to_string()), config.clone()))
+            .collect();
+
+        for (name, tcp_config) in tcp_instances {
+            let transport_id = self.allocate_transport_id();
+            let tcp = TcpTransport::new(transport_id, name, tcp_config, packet_tx.clone());
+            transports.push(TransportHandle::Tcp(tcp));
+        }
+
         transports
     }