feat: punkt 5 (monitoring) — system dashboard backend+frontend, admin-only, auto-refresh 30s, alerting via notifications

frontend/src/components/layout/Sidebar.tsx

@@ -55,6 +55,7 @@ const singleItems: NavSingleItem[] = [
   { to: '/dashboard', labelKey: 'nav.dashboard', icon: <Home className="w-5 h-5 flex-shrink-0" aria-hidden="true" strokeWidth={2} />, order: 0 },
   { to: '/contacts', labelKey: 'nav.contacts', icon: <Users className="w-5 h-5 flex-shrink-0" aria-hidden="true" strokeWidth={2} />, order: 10 },
   { to: '/wiki', labelKey: 'nav.wiki', icon: <BookOpen className="w-5 h-5 flex-shrink-0" aria-hidden="true" strokeWidth={2} />, order: 30 },
+  { to: '/system-dashboard', labelKey: 'nav.systemDashboard', icon: <Activity className="w-5 h-5 flex-shrink-0" aria-hidden="true" strokeWidth={2} />, order: 90 },
 ];
 
 const bottomItems: NavSingleItem[] = [];
@@ -209,6 +210,8 @@ export function Sidebar() {
               for (const item of singles) {
                 // Skip if user lacks permission
                 if (item.permission && !canAccess(item.permission)) continue;
+                // Skip admin-only items for non-admins
+                if (item.path === '/system-dashboard' && !user?.is_system_admin) continue;
                 elements.push(
                   <li key={item.path}>
                     <NavLink