The run time booted after like ... 10 minutes.
It was pretty cool - there was an android device (Nexus?) running on my desktop in its own window.

BUT I couldn't run my app because ... no Android SDK was selected.  So when I installed the packages containing the run-time I foobared my environment, apparently.

I've quit IntelliJ, deleted the project, and restarted IntelliJ to create a fresh project.  Hopefully, the Android SDK will be selected properly.