docs: rebuild landing page, update facts and add GEO/SEO + live releases

- Update to current capabilities: 158 languages, 11 agents, 14 MCP tools,
  Hybrid LSP, infrastructure-as-code indexing, single static C binary
- Add dedicated Hybrid LSP section and per-language resolution table
- Remove the GitNexus comparison
- Restructure with answer-first, question-based headings for AI answer engines
- Add JSON-LD structured data (SoftwareApplication, Organization, WebSite,
  BreadcrumbList, FAQPage) with arXiv preprint citation
- Add a live GitHub releases widget (client-side, graceful fallback)
- Add prominent research-preprint callout under the hero
- Centered nav, "by DeusData" subtitle, inline SVG favicon
- Welcome AI crawlers in robots.txt, refresh sitemap, add llms.txt
- Fix broken benchmark link

Author: DeusData