Implement SSH Phase 13.4: Port forward listener thread

- Create port_forward_listener.rs module (246 lines)
- Define PortForwardListener structure
- Implement ListenerRequest/ListenerResponse for thread communication
- Implement ListenerManager for managing multiple listeners
- Create start_listener_thread() for independent listener thread
- Implement GatewayPorts binding address logic
- Add thread synchronization (Arc<Mutex<bool>>)
- Support NewConnection and StopListener requests
- All compilation tests passed successfully

Phase 13.1-13.4 completed: Security + Global request + Channel + Listener thread

markbase-core/src/ssh_server/mod.rs

@@ -16,6 +16,7 @@ pub mod scp_handler;
 pub mod rsync_handler;
 pub mod port_forward;           // Phase 13: 端口转发模块
 pub mod ssh_security_config;    // Phase 13.1: 企业级安全配置
+pub mod port_forward_listener;  // Phase 13.4: 监听线程模块
 
 pub use server::SshServer;
 pub use packet::{SshPacket, PacketType};