Fix mobile nav visibility and stale stats link; add nginx security headers to config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/header.html

@@ -26,7 +26,7 @@
 
   <!-- Nav row -->
   <div class="navbar bg-base-200 px-4 min-h-0 py-2">
-    <div class="navbar-center flex flex-1 justify-center">
+    <div class="navbar-center hidden lg:flex flex-1 justify-center">
       <ul class="menu menu-horizontal px-1 gap-1">
         <li><a href="/index.html">Home</a></li>
         <li><a href="/signups.html">Sign-ups</a></li>
@@ -54,7 +54,7 @@
           <li><a href="/index.html">Home</a></li>
           <li><a href="/signups.html">Sign-ups</a></li>
           <li><a href="/reporting.html">Game Reporting</a></li>
-          <li><a href="/stats.html">Stats</a></li>
+          <li><a href="/standings.html">Standings</a></li>
         </ul>
       </div>
     </div>