feat: separate About/Clients/Partners into /o-kompanii/ page, add IndexNow meta

- Create /[lang]/o-kompanii/ page with About, Clients, Partners sections
- Remove those sections from homepage (Hero + Services + FAQ remain)
- Update Header nav: "О нас" now links to /o-kompanii/ instead of /#about
- AboutSection: support standalone prop (h1 vs h2)
- Root layout: add indexnow-key meta tag (key from public/40c65b...txt)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/layout/Header.tsx

@@ -14,7 +14,7 @@ export default function Header({ lang }: { lang: string }) {
 
   const links = [
     { label: d.nav.services, href: `/${lang}/uslugi/` },
-    { label: d.nav.about, href: `/${lang}/#about` },
+    { label: d.nav.about, href: `/${lang}/o-kompanii/` },
     { label: d.nav.faq, href: `/${lang}/faq/` },
   ]