Fix TypeScript compilation error in BibleReader

- Added null check for verseNumber before rendering favorite button
- Prevents 'string | null is not assignable to string' error

frontend/src/components/BibleReader.tsx

@@ -267,7 +267,7 @@ const BibleReader: React.FC<BibleReaderProps> = ({ book, chapter, onBack, format
               <span className="bible-text">{verseText}</span>
             </div>
             {/* Star button - only show for authenticated users */}
-            {user && (
+            {user && verseNumber && (
               <button
                 onClick={() => toggleFavorite(verseNumber)}
                 className="ml-2 mt-1 p-1 rounded hover:bg-gray-200 dark:hover:bg-gray-600 transition-colors"