Add user information and calendar list to sidebar

Backend changes:
- Add /api/user/info endpoint to fetch user details and calendar list
- Create UserInfo and CalendarInfo models for API responses
- Filter out generic calendar collections from sidebar display
- Extract readable calendar names with proper title case formatting

Frontend changes:
- Fetch and display user info (username, server URL) in sidebar header
- Show list of user's calendars with hover effects and styling
- Add loading states and error handling for user info
- Reorganize sidebar layout: header, navigation, calendar list, logout

Styling:
- Enhanced sidebar with user info section and calendar list
- Responsive design hides user info and calendar list on mobile
- Improved logout button positioning in sidebar footer
- Professional styling with proper spacing and visual hierarchy

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/lib.rs

@@ -37,6 +37,7 @@ pub async fn run_server() -> Result<(), Box<dyn std::error::Error>> {
         .route("/api/health", get(health_check))
         .route("/api/auth/login", post(handlers::login))
         .route("/api/auth/verify", get(handlers::verify_token))
+        .route("/api/user/info", get(handlers::get_user_info))
         .route("/api/calendar/events", get(handlers::get_calendar_events))
         .route("/api/calendar/events/:uid", get(handlers::refresh_event))
         .layer(