feat: improve SEO with locale-specific metadata, structured data, and keywords

- Add locale-specific title/description for DE and EN homepage
- Expand keywords with local SEO terms (Webentwicklung Osnabrück, Informatik, etc.)
- Add WebSite schema and enhance Person schema with knowsAbout, alternateName
- Add hreflang alternates for DE/EN
- Update projects page with locale-specific metadata
- Keep visible titles short, move SEO terms to description/structured data

app/[locale]/projects/page.tsx

@@ -13,7 +13,12 @@ export async function generateMetadata({
 }): Promise<Metadata> {
   const { locale } = await params;
   const languages = getLanguageAlternates({ pathWithoutLocale: "projects" });
+  const isDe = locale === "de";
   return {
+    title: isDe ? "Projekte – Dennis Konkol" : "Projects – Dennis Konkol",
+    description: isDe
+      ? "Webentwicklung, Fullstack-Apps und Mobile-Projekte von Dennis Konkol. Next.js, Flutter, Docker und mehr – Osnabrück."
+      : "Web development, fullstack apps and mobile projects by Dennis Konkol. Next.js, Flutter, Docker and more – Osnabrück.",
     alternates: {
       canonical: toAbsoluteUrl(`/${locale}/projects`),
       languages,