Finally, finally, found a bot for Quake 4 that works with Windows and Linux with minimal tweaking. Behold, Stupid Angry Bot!
To install, create a folder inside the Quake 4 folder called "sabot" and unzip the files into it. Run the batch file "Load Sabot" in the sabot folder or start Quake 4 with "+ set fs_game sabot" and create a new multiplayer game (scripts are available to this at the command line too).
To add a bot bring down the console (via the CTRL-ALT-TILDE (~) keys) and type: addbot bot_sabot
Read the included README files for more advanced options.