Localize the VitePress docs into Simplified Chinese, Spanish, Japanese,
French and German (18 pages each), mirroring the existing en/ru structure.
- generate the 5 new locales in config.ts from a single strings table
(nav, sidebar, search, footer, docFooter, outline, editLink) with
locale-prefixed links
- rework DocsCardGrid from the binary isRu check to a per-locale map so
the home cards render translated copy and prefixed links for every locale
