fix(leaderboard): fix accuracy table header missing on small screens (@fehmer) (monkeytypegame#6739)

Before:
<img width="967" height="147" alt="image"
src="https://github.com/user-attachments/assets/ca1b176f-47e6-48d3-9f2a-c34a3896ecd4"
/>

After:
<img width="1177" height="181" alt="image"
src="https://github.com/user-attachments/assets/2749d4b6-1799-46fb-8946-f16a417002a8"
/>

Author: fehmer

frontend/src/html/pages/leaderboards.html

@@ -52,7 +52,7 @@
             <td>#</td>
             <td>name</td>
             <td class="stat narrow speedUnit">
-              wpm
+              <span>wpm</span>
               <div class="sub">accuracy</div>
             </td>
             <td class="stat narrow rawAndConsistency">

frontend/src/ts/pages/leaderboards.ts

@@ -922,7 +922,7 @@ function updateContent(): void {
   fillTable();
 
   for (const element of document.querySelectorAll(
-    ".page.pageLeaderboards .speedUnit"
+    ".page.pageLeaderboards .wide.speedUnit, .page.pageLeaderboards .narrow.speedUnit span"
   )) {
     element.innerHTML = Config.typingSpeedUnit;
   }