Set up Vitest and add basic React tests

[krgjert]

Add a small set of meaningful tests covering the different testing types required for Project 1.
Tasks

• Set up Vitest and React Testing Library.
• Add at least one snapshot test, e.g. for DriverCard.
• Test component rendering with different props.
• Test initial state and state changes after interaction, e.g. toggling favorites.
• Test user interactions, e.g. searching or clicking Next.
• Mock API calls so tests do not fetch real data.
• Manually test the UI on available desktop browsers and mobile devices.
• Document how to run the tests and the manual testing results.
  Acceptance criteria

Tests pass and demonstrate snapshot testing, props, state, user interactions, and mocking. Focus on trying the different testing methods rather than reaching a specific number of tests.