fix(explorer): show unknown if no aggregator set in aggregated proof view (#1922)

Author: JuArce

explorer/lib/explorer_web/live/pages/agg_proof/index.html.heex

@@ -31,6 +31,8 @@
             <p>SP1</p>
           <% :risc0 ->  %>
             <p>RISC0</p>
+          <% _ -> %>
+            <p>Unknown</p>
         <% end %>
       </div>