I figured it out. I just needed to add ‘onsen’ to the angular.module list argument. Fortunately, my teammate on this project understands Angular better than I do.
There’s a perfectly good example in the OnsenUI github, too: https://github.com/OnsenUI/onsenui2-quickstart/blob/master/www/angular/app.js
I didn’t realize when I first looked at it that that was in there. Once I found it, it made things much clearer.