We are about to add overrides of gui.theme for dark and light
backgrounds. Author and branch colors need them too, because a color
that reads well on a dark background may be hard to read on a light
one. Move them into gui.theme, so that the overrides cover them without
a mechanism of their own.
The migration of gui.branchColors creates gui.branchColorPatterns, so it
now has to run before the moves.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>