test: add frontend quality foundation

client/README.md

@@ -30,3 +30,25 @@ If you are developing a production application, we recommend enabling type-aware
 ```
 
 See the [Oxlint rules documentation](https://oxc.rs/docs/guide/usage/linter/rules) for the full list of rules and categories.
+
+## Quality checks and tests
+
+Run the frontend checks from `client/`:
+
+```bash
+npm ci
+npm run format:check
+npm run lint
+npm run test
+npm run build
+```
+
+The test suite uses Vitest, jsdom and React Testing Library. It currently
+covers the shared header snapshot, active navigation state, place-card props
+and interactions, home-page selection and list controls, and the loading,
+error and in-memory cache behaviour of `useFetch`.
+
+Tests use fixed data and mocked hooks rather than external requests. The
+snapshot protects the header's rendered HTML structure; it is not a pixel-level
+visual regression test for CSS. Visual screenshot tests should use one fixed
+browser environment to avoid differences between operating systems.