auto-claude: subtask-3-3 - Fix robots.txt and sitemap configuration

- Remove outdated static public/sitemap.xml that conflicted with dynamic sitemap.ts
  (was missing leistungen pages, city pages, and had outdated blog/portfolio slugs)
- Fix robots.ts to reference only the single sitemap.xml instead of non-existent
  language-specific sitemaps (sitemap-de.xml, sitemap-en.xml, sitemap-sr.xml)
- Dynamic sitemap.ts now handles all pages with proper hreflang alternates

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/robots.ts

@@ -12,11 +12,6 @@ export default function robots(): MetadataRoute.Robots {
         crawlDelay: 1,
       },
     ],
-    sitemap: [
-      `${baseUrl}/sitemap.xml`,
-      `${baseUrl}/sitemap-de.xml`,
-      `${baseUrl}/sitemap-en.xml`,
-      `${baseUrl}/sitemap-sr.xml`,
-    ],
+    sitemap: `${baseUrl}/sitemap.xml`,
   };
 }