eigen_shell is the complete, opinionated EigenInteractive Flutter app: app
startup, routing, sign-in, home, lobby, game chrome, history and replay,
friends, profile, settings, notifications, updates, and theming.
Game rules and rendering depend on eigen_flutter,
which remains embeddable and does not own a root MaterialApp. Applications
that want the standard product import this package and call runEigenShell.
See the EigenInteractive documentation for the complete server-and-client setup.