feat(ui): add collapsible sidebar functionality

Implement a collapsible sidebar feature for the desktop view that allows
users to toggle between expanded and collapsed states. The sidebar state
is persisted using localStorage to maintain user preference across
sessions.

Changes include:
- Add sidebarVisible state with localStorage persistence
- Import Sparkles and SettingsIcon from lucide-react
- Implement smooth transition animation (300ms) for sidebar collapse
- Add collapsed sidebar view with icon-only navigation buttons
- Pass onToggleSidebar prop to Sidebar component
- Adjust sidebar width dynamically (80 -> 14 when collapsed)

This improves the user experience by providing more screen real estate
for the main content area when needed, while keeping quick access to
essential navigation through the collapsed icon view.

src/components/ChatInterface.jsx

@@ -514,7 +514,6 @@ const MessageComponent = memo(({ message, index, prevMessage, createDiff, onFile
                               <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M19 9l-7 7-7-7" />
                             </svg>
                             <span className="flex items-center gap-2">
-                              <span className="text-lg leading-none">📝</span>
                               <span>View edit diff for</span>
                             </span> 
                             <button