Frontend:
- Add sidebarOpen state to chatStore with toggle functionality
- Make sidebar collapsible with smooth animation
- Add mobile-friendly drawer behavior with overlay
- Add toggle button for desktop view
- Implement delete conversation functionality with loading state
Backend:
- Add DELETE /conversations/:id endpoint
- Implement deleteConversation service method
- Delete messages before conversation (foreign key constraint)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>