I have a Navigation Bar!
After wasting an entire day trying to restore the Navigation Bar (the bar at the top with the search window and the "Sign In" option), I finally copied just one line of code from Katharine's blog, et voilà.
I have a Navigation Bar.
I have now spent an entire day of my life losing my template, finding an ancient backed-up copy of my template, restoring my template, researching how to restore a Navigation Bar and, finally, actually restoring my Navigation Bar.
I should apply for a job at Mycollege's Help Desk.
For future reference, the navigation bar is one line of code: