If you open the q3config.cfg file, you’ll see the line bind ESCAPE "togglemenu". What you want to do is to add a file named autoexec.cfg beside it, and put unbind ESCAPE in the newly created file.
But you should probably also keep a way to toggle the menu. For that, add another line bind F12 "togglemenu" in autoexec.cfg (or with another key instead of F12).