- Added SIGINT signal handler to wsscp.c for proper signal handling
- Modified execute_scp_command() to fork/exec instead of using system()
- Added process tracking with scp_pid global variable
- Signal handler sends SIGTERM to SCP process when Ctrl+C is received
- Added proper cleanup and exit code handling for interrupted transfers
- Ensures wsssht (ProxyCommand) gets time to send tunnel_close message
- Prevents orphaned processes and ensures clean tunnel closure

This resolves the issue where Ctrl+C on wsscp didn't allow the underlying wsssht process to send tunnel_close messages to the server.