What changed

• add Vitest, jsdom and React Testing Library
• add a reviewed snapshot of the shared site header
• test active navigation state
• test place-card props and previous/next interactions
• test home-page selection and list controls with mocked hooks
• test loading, error and in-memory cache behaviour in useFetch
• document the frontend quality commands

The tests use fixed data and do not make external requests. No production application code is changed.

Verification

• npm ci
• npm run format:check
• npm run lint
• npm run test — 8 tests passed
• npm run build
• git diff --check