New /scp page with form for host, user, password, remote path.
Runs scp via sshpass in background with progress polling.
Files go to /mnt/converter/in/{session_id}/ for multi-user isolation.
- Added sshpass + openssh-client to frontend installer
- scp.html template with full form + progress bar
- POST /scp/start — launches background SCP via sshpass -e
- GET /scp/progress/{sid}/{file} — polls file size + speed
- 'SCP Pull (+10 GB)' button on start page
