It turns out the THREE.js animation system is a total nightmare.  Hopefully I’ll look back on this fondly in a few months and think, “What a fool I was.  The animation system is actually very powerful and really simple!”  For now, though, it’s rough.  The primary issue is that this very, very brief overview of the system is the only real up to date information I can find online about the it.  The animation system in THREE.js changed radically somewhere around r69 or r70 so there is some information about the old system, but that really does me no good.  I think that the best thing here is to just write my own tutorial covering everything from exporting a mesh from Blender to running specific clips in a scene.  Writing a tutorial will force me to understand the system a little better, and also hopefully create a resource for others who might be struggling with this, so keep your eyes open for that over the next several days.