Project: fastify
Task (challenging): 1) Add a client-side component in public/components/HeaderUserMenu.js:
   - If not logged in, display a button (.header-go-login) that navigates to /login
   - If logged in, display the username (.header-username)
2) If user is logged in, when the .header-username is hovered, show a dropdown menu with:
   - A button (.header-logout-btn) for logging out
   - A button (.header-go-user-profile) for navigating to the current user's profile page
3) Ensure that this component is displayed on the right side of the site header
4) Create CSS to beautify UI
5) DO NOT use a third-party UI library