Support reduced-motion animations

[dendrochronology]

First response: this is awesome! Until I get dizzy, a mild headache, and feel like I might barf 🤮

It would be rad if there was a reduced-motion animation (maybe jump points with subtle fades/wiggles?), that automatically kicked in on matchMedia('(prefers-reduced-motion)')

[jdsteinbach]

An on-brand way to handle reduced motion could be:

• Doors close from R/L edges of screen
• Music plays, bell dings
• Doors open at top of page