This commit introduces the frontend implementation to handle API responses for features that have been moved (301) or split (410). This builds upon previous backend changes that enabled the API to return these status codes.

On the client side:
- For a 301 response, the feature page now performs a client-side redirect. It catches a `FeatureMovedError`, updates its state with the new feature's data from the response body, and uses `history.pushState` to update the URL. This provides a smooth user experience without a full page reload. A notice is also displayed to inform the user of the redirect.

- For a 410 response, the feature page redirects to a dedicated "Feature Gone" page, which explains that the feature was split and provides the user with links to the new features.

As this is a Single Page Application (SPA), the client-side fetch determines whether a redirect or a "gone" page is necessary. This approach is a trade-off for better UX within the SPA architecture.

Unit and end-to-end tests have been added to cover these new scenarios.