Hi, first off, servers deployed with Forge should already be set up for pretty url's. Take a look in the file
/etc/nginx/sites-enabled/default
and you will see this:
location / {
try_files $uri $uri/ /index.php?$query_string;
}
The reason why you can't edit these files that are root-owned with Cyberduck is because you need root privileges as you said. You can accomplish the editing of these files (although normally not needed) by using a terminal program (Terminal.app or iTerm on a mac or Putty on a Windows PC). If you then use a command like this:
sudo vim /etc/nginx/sites-enabled/default
or perhaps easier if you've never used vim before:
sudo nano /etc/nginx/sites-enabled/default
On your first attempt, it will ask you for a password. This is the 'sudo password' that is provided in the mail sent by Forge when your server was first set up.
Hope that helps. /K