fix: don't fetch docs until annotatorName is set

Prevents race condition where docs are fetched with no user filter
before the HF cookie is read, causing a flash of all documents.

app/page.js

@@ -51,10 +51,11 @@ export default function Home() {
 
     // Load documents (re-fetches when annotatorName changes to get user-specific assignment)
     useEffect(() => {
+        // Don't fetch until we know who the user is — avoids showing all docs briefly
+        if (!annotatorName) return;
+
         setLoading(true);
-        const url = annotatorName
-            ? `/api/documents?user=${encodeURIComponent(annotatorName)}`
-            : '/api/documents';
+        const url = `/api/documents?user=${encodeURIComponent(annotatorName)}`;
 
         fetch(url)
             .then(res => res.json())