Add logout functionality and implement persistent user sessions

Add a logout option ensure user sessions persist properly across page refreshes.

Current State:

• User can log in (username shows in top right)
• No logout option available
• Sessions may not persist after page reload
• No handling for session expiration

Requirements:

1. Add a logout button/option to the UI
2. Implement proper session management so logged-in users stay logged in after page refresh
3. Clear session data when user logs out and redirect to login page
4. Handle session expiration automatically:
   • Show popup/notification when session expires
   • Automatically redirect to login form after session timeout
   • Display appropriate message to user about session expiration

Acceptance Criteria:

• Logout button/link is visible when user is logged in
• Clicking logout clears the session and redirects to login
• User sessions persist across page reloads
• Username remains visible in navigation after refresh
• Session expiration is detected automatically
• Popup/notification appears when session expires
• User is redirected to login form after session timeout