Splits the landing page into / and /ru/ so each language can rank on
its own, with hreflang links between them; boot.js/main.js now do a
real navigation between the two instead of toggling text in place.
Adds robots.txt and sitemap.xml, JSON-LD SoftwareApplication markup,
Twitter Card tags, and a proper 1200x630 og-image.png in place of the
SVG favicon for social previews.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
