- Implement bidirectional pipe communication for VNC sessions
- Replace single pipe with separate stdin/stdout pipes
- Fix child process redirection to properly handle both input and output
- Add enhanced debug logging for VNC data flow
- Update resource cleanup in vnc_free_session()

This resolves the issue where VNC connections would hang after exchanging
the first 12 bytes (RFB protocol version strings) because input from
noVNC WebSocket wasn't reaching the wsssht process.