refactor(session): add registry to manage SSH sessions

- Implement thread-safe session registry with sync.RWMutex
- Add Registry interface for session management operations
- Support Get, Register, Update, and Remove session operations
- Enable dynamic slug updates for existing sessions
- Fix Connection closed by remote because HandleTCPIPForward run on a goroutine

session/session.go

@@ -92,7 +92,7 @@ func (s *SSHSession) Start() error {
 	s.lifecycle.SetChannel(ch)
 	s.interaction.SetChannel(ch)
 
-	go s.HandleTCPIPForward(tcpipReq)
+	s.HandleTCPIPForward(tcpipReq)
 
 	if err := s.lifecycle.Close(); err != nil {
 		log.Printf("failed to close session: %v", err)