background: change "Light" to "Default"
Addresses concerns raised in #1731 (closed) by changing the label of the default
color scheme setting to "Default" instead of "Light".
Doesn't currently change any variable names, though I think I'll do a pass so it's less confusing if/when an explicit Doneprefer-light
toggle is actually added.
Doesn't attempt to explain or redesign things further or affect any other UI.
Edited by Cassidy James Blaede