Adds the third button to the language tray in /settings; the local state
union widens to 'en' | 'es' | 'eu' (matches the new LanguageCode). Each
button carries a stable `settings-language-{code}` testid for the e2e
hooks.
Playwright `tests/e2e/euskera.test.ts`:
* EU-01 — Ana clicks the eu button; assertion lands on the selected-
state class flip (synchronous proof the click reached
switchLanguage) + a DB poll for `users.language='eu'`. We
deliberately don't assert on the sidebar nav label re-rendering:
ParaglideJS's {#key lang} re-render is wired to URL routing, not
the runtime setLanguageTag call, so the visible labels only flip on
the next navigation — a known cross-cutting gap outside Fase 20's
scope.
* EU-02 — Fresh browser context with locale + Accept-Language=eu;
Eva logs in fresh and the Fase 10.8 bootstrap path UPDATEs
users.language to 'eu'. /onboarding renders 'Ongi etorri…' — the
Basque heading the seed produces. Cleanup restores Ana to seed 'es'.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
