Created comprehensive sidebar navigation documentation in docs/sidebar-navigation.md. **Documentation covers:** - Sidebar states (collapsed vs expanded) - Navigation elements: Logo/Home, New Thread (+), Library, Account, Upgrade, Install - Notifications panel layout and item format - Interaction patterns (hover, click, keyboard) - Responsive behavior for desktop/tablet/mobile - Visual specifications (colors, typography, spacing) - Implementation notes (accessibility, state management, animation) **Excluded per requirements:** Discover, Spaces, Finance, More features **Screenshots analyzed:** - 01_home_page.png - Collapsed sidebar state - 07_sidebar.png - Expanded sidebar with notifications - 05_library_view.png - Library context - 06_notifications.png - Notifications panel detail **Files changed:** - Created: docs/sidebar-navigation.md - Updated: README.md (added reference to docs and updated project structure)