Visiting the app with no hour in the URL previously always showed
Prime for today, since selectedHour was hardcoded in AppState. Now it
picks the hour whose band contains the visitor's local clock time.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L3wxvz3mPXiHxkPB5JpnmD
