A failed write leaves the old file in place. Settings that could not be read
are not saved over. UI exceptions reach the log. Started from a shortcut set
up elsewhere, the starter moves to its own folder when only that one holds a
game.
VehicleDatabase becomes VehicleCatalog, Physics becomes VehiclePhysics, and the
textures.txt and .fiz parsers move to Infrastructure. GameLibrary replaces the
GameData singleton.