Black Plane Skybox

Add 1 new skybox to the lighting menu - Black Plane

This increases contrast like a shadow/darkbox, creates more separation for the map to the background, and allows for shadows off-map to disappear instead of casting onto the parchment texture.

The black plane would be a simple skybox option with the same lighting controls we currently have, and allow us to create these “isolated” segments of world, where the player can fill in the blanks with their imaginations.

It also means “open paths” feel more “mysterious”.