- Add model selector to ChatView component for AI model selection
- Update ChatView tests to cover model selector functionality
- Add styles for model selector in chat interface
- Add ChatView component with sidebar navigation and message thread layout
- Add useChat hook with SSE streaming state management for real-time updates
- Add chat API functions for sessions and messages (create, list, send, stream)
- Add mobile-responsive CSS styles for chat interface
- Add tests for useChat hook and ChatView component
- Integrate chat into task view and navigation (Header, MobileNavBar)
