Private instances can gate the dashboard behind login with HIVE_VISIBILITY

Hive can now require authentication before anyone can reach the dashboard. Set HIVE_VISIBILITY=private to gate the app behind login, or leave it as public for open access. The dashboard routes use a new RequireAuthenticated plug that redirects unauthenticated visitors to the login page and remembers where they were going. Source: the release notes list this under ⛰️ Features, and lib/hive_web/plugs/require_authenticated.ex plus lib/hive/auth.ex implement the HIVE_VISIBILITY check.