v2.0.0-beta.1 — the folder config authority (next channel)

Backfilled entry. ~/.rbox/config.json became the single readable authority for which folders each machine syncs and their options (design 231): open it, edit it, the daemon applies it. Machines upgrading with existing folders run rbox config regenerate once. New commands: rbox config / add / regenerate / repair. Install: rbox upgrade --channel next.