Update button text in TopBar component

Revised the button label from "Neues Spiel" to "✦ Neues Spiel" to enhance visual appeal and draw user attention. This minor UI tweak improves the user experience.

frontend/src/components/TopBar.jsx

@@ -51,7 +51,7 @@ export default function TopBar({
         </div>
 
         <button onClick={newGame} style={styles.primaryBtn}>
-          + Neues Spiel
+          ✦ Neues Spiel
         </button>
       </div>
     </div>