- Update `destroy` action in `SessionsController` to log out
only if the user is currently logged in.
- Add a check in the `authenticated?` method of the `User`
model to return false if `remember_digest` is nil.
- Enhance integration tests to simulate logout in another
browser session and verify that the logout link is not
present after logging out.
These changes improve the robustness of the session management
by preventing unnecessary logout attempts and ensuring that
authentication checks are more reliable.