fix(reaction): materialize paginated queryset before JSON response

ReactionStatsAPI called the sync paginate_data() without an
object_serializer, leaving results as a lazy QuerySet. json.dumps()
in JSONResponse.response has no custom encoder for QuerySet, so every
request 500'd. list() the results before wrapping in success().

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

reaction/views/admin.py

@@ -36,4 +36,6 @@ class ReactionStatsAPI(APIView):
             order_by = DEFAULT_ORDERING
 
         queryset = queryset.order_by(order_by)
-        return self.success(self.paginate_data(request, queryset))
+        data = self.paginate_data(request, queryset)
+        data["results"] = list(data["results"])
+        return self.success(data)