style: deeper purple + remove redundant page title

- Darkened primary from #8b5cf6 to #6d28d9 (violet-700) to better
  complement the dark theme
- Removed <h1> page title — the sidebar active highlight already
  tells you which tab you're on
- Cleaned up related CSS and elTitle plumbing in app.js

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

js/app.js

@@ -8,7 +8,6 @@
   var elConnected = document.getElementById('app-connected');
   var elHeader = document.getElementById('server-header');
   var elSidebar = document.getElementById('sidebar-nav');
-  var elTitle = document.getElementById('page-title');
 
   // ---- Sidebar navigation ----
   var navPages = [
@@ -30,7 +29,6 @@
 
   function setActivePage(title) {
     window._currentPage = title;
-    elTitle.textContent = title;
     if (Rcon.isConnected()) renderSidebar(Rcon.getAddress());
   }