feat(sidebar): fleet sidebar standard (header row, user in sidebar, collapsible groups, mini mode, no-flash transitions)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

views/sysadmin/system_settings.php

@@ -128,7 +128,6 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 }
 
 include __DIR__ . '/../../includes/header.php';
-include __DIR__ . '/../../includes/navbar.php';
 ?>
 <div class="container py-4" style="max-width:900px;">
     <div class="d-flex justify-content-between align-items-center flex-wrap gap-2 mb-3">