fix(surprise-me): change default algorithm to weighted_random

- Update initial algorithm state from 'unwatched_first' to 'weighted_random'
- Adjust SurpriseMePage to use new default recommendation algorithm

src/app/surprise-me/page.tsx

@@ -14,7 +14,7 @@ const ALGORITHMS = [
 ] as const;
 
 export default function SurpriseMePage() {
-  const [algorithm, setAlgorithm] = useState<Algorithm>('unwatched_first');
+  const [algorithm, setAlgorithm] = useState<Algorithm>('weighted_random');
   const [recommendations, setRecommendations] = useState<any[]>([]);
   const [isLoading, setIsLoading] = useState(true);
   const [selectedVideo, setSelectedVideo] = useState<any>(null);