Replace blocking event loop with tokio::select! over EventStream, mpsc
channel, and tick interval. Add message bus architecture with AppMessage
enum for background task results. Implement Dashboard with roster summary
cards and API sync, and Gameday with cascading team/pitcher selectors,
matchup table, and 9-slot lineup management with save/load.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
