💚 Fix new healthz route syntax error

Author: baptisteArno

apps/viewer/src/app/healthz/route.ts

@@ -1,8 +1,8 @@
-export default function GET() {
+export const GET = async () => {
   return new Response(
     JSON.stringify({ status: "ok", timestamp: new Date().toISOString() }),
     {
       headers: { "Content-Type": "application/json" },
     },
   );
-}
+};