Add winner display name support in game metadata

Updated backend to include winner's display name in the game metadata API and frontend to display it alongside the email. This enhances clarity by showing a more user-friendly identifier.

frontend/src/App.jsx

@@ -411,7 +411,12 @@ export default function App() {
         />
 
         {/* Sieger Badge: zwischen Spiel und Verdächtigte Person */}
-        <WinnerBadge winnerEmail={gameMeta?.winner_email || ""} />
+        <WinnerBadge
+          winner={{
+            display_name: gameMeta?.winner_display_name || "",
+            email: gameMeta?.winner_email || "",
+          }}
+        />
 
         <HelpModal open={helpOpen} onClose={() => setHelpOpen(false)} />