const HABITABLE_INSOLATION: { inner: 2000; outer: 800 }
The insolation band this build calls habitable, W/m².
A pair of constants rather than two literals inside isHabitable, because
the planetarium draws the band as a distance and the generator tests a body
against it, and a panel that answered from its own numbers would eventually
shade a ring the simulation disagreed with. Earth receives about 1361.