fix: serverInfo page shows data immediately on load

Eliminated redundant serverinfo RCON polling from the serverInfo page.
It now subscribes to the header's serverinfo-update CustomEvent instead.

Key changes:
- app.js: cache last serverinfo in window._lastServerInfo and dispatch
  serverinfo-update event so pages can pick up data immediately
- serverInfo.js: replaced setInterval-based polling with event listener
  plus immediate _lastServerInfo cache check, eliminating the initial
  blank page state and duplicate RCON requests

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

js/app.js

@@ -46,6 +46,10 @@
       document.getElementById('header-players').innerHTML = '<i class="bi bi-people-fill"></i> ' + formatNumber(data.Players) + '/' + formatNumber(data.MaxPlayers);
       document.getElementById('header-fps').innerHTML = '<i class="bi bi-speedometer2"></i> ' + formatNumber(data.Framerate) + 'fps';
       document.getElementById('header-entities').innerHTML = '<i class="bi bi-boxes"></i> ' + formatNumber(data.EntityCount);
+
+      // Cache for late-arriving pages (e.g. serverInfo) and broadcast to listeners
+      window._lastServerInfo = data;
+      document.dispatchEvent(new CustomEvent('serverinfo-update', { detail: data }));
     });
   }