How do I set a password for a newly created agent when I do not want to send them an activation email?

When creating the agent, click 'Set Password'. In the password dialog, uncheck the 'Send Welcome Email' (or 'Send Password Reset Email') checkbox -- this reveals the password input fields. Enter the password directly and save. If the agent account already exists, go to their profile, click 'Reset Password', uncheck the email option in the popup, and set the password manually.