feat(legal): bilingual (RU + EN) legal pages with a language + theme switcher

Add English versions of the privacy policy, EULA and offer (ui/legal/*_en.md) and render each legal page as one self-contained bilingual document: both language bodies plus a header language toggle and theme toggle (no back), a small inline ES5 script that switches language client-side (no reload, default Russian + persisted) and applies the theme (system default + persisted override) — mirroring the landing. The offer's English view transliterates the Russian product names spliced from the live catalog.

renderLegalHtml now takes both language sources; renderOffer splices the price list into both; the renderer bakes and reads the _en sources and pre-renders the static pages at boot. Also wrap the /offer/ contour probe in the same retry+timeout as the legal probe (the offer page is now bilingual and larger). Docs + renderer/ui tests updated.

renderer/Dockerfile

@@ -27,7 +27,7 @@ COPY renderer/src/server.mjs renderer/src/render.mjs renderer/src/offer.mjs rend
 # The public legal pages: the owner-edited markdown, read once at boot. GET /offer/ also splices in
 # the live price list fetched from the backend at request time; GET /privacy/ and GET /eula/ are
 # static (no dynamic data).
-COPY ui/legal/offer_ru.md ui/legal/privacy_ru.md ui/legal/eula_ru.md ./legal/
+COPY ui/legal/offer_ru.md ui/legal/offer_en.md ui/legal/privacy_ru.md ui/legal/privacy_en.md ui/legal/eula_ru.md ui/legal/eula_en.md ./legal/
 USER node
 EXPOSE 8090
 CMD ["node", "src/server.mjs"]