- Implement double SIGINT (Ctrl+C) detection in wssshd server
- First Ctrl+C: Initiates graceful shutdown with cleanup
- Second Ctrl+C: Forces immediate exit using os._exit(1) without cleanup
- Consistent behavior with wssshc double Ctrl+C handling
- Prevents hanging during shutdown when graceful shutdown fails
- Maintains backward compatibility with single Ctrl+C graceful shutdown

This ensures wssshd can be forcefully terminated if graceful shutdown gets stuck, while still allowing proper cleanup on normal shutdown.