fix: use plain <a> for static file links to avoid RSC 404

Paths with file extensions (e.g. /llms.txt) are static files in
public/, not Next.js routes. next/link prefetches them as RSC flight
requests (?_rsc=) which 404. Detect file extensions in Link and
render a plain <a> tag instead.

Author: quantizor

components/Link.tsx

@@ -80,7 +80,7 @@ export default function Link({ children, href, variant = 'block', target, ...res
   const resolved = variant;
 
   const hrefString = typeof href === 'string' ? href : href?.toString() || '';
-  const isExternal = hrefString.startsWith('http') || hrefString.startsWith('//');
+  const isExternal = hrefString.startsWith('http') || hrefString.startsWith('//') || /\.\w+$/.test(hrefString);
   const finalTarget = target || (isExternal ? '_blank' : undefined);
   const rel = isExternal ? 'noopener' : undefined;