Tool-detail pages (/tools/<section>/<tool>/) and the /self-hosted pages are
built only in English, with no per-locale route, so a locale-prefixed link
404s in the static build. Add an enOnlyHref() helper and use it for those
links in Footer, Navbar, HeroSearch, and ToolGrid so localized pages point at
the English pages that actually exist. Adds an e2e guard asserting localized
pages emit un-prefixed URLs for those routes.
