feat(ui): toggleable settings sidebar + back-to-start arrow in TopBar

frontend/src/components/layout/TopBar.tsx

@@ -8,7 +8,7 @@ import { useLogout } from '@/api/hooks';
 import { Avatar } from '@/components/ui/Avatar';
 import { SearchDropdown } from '@/components/shared/SearchDropdown';
 import { SuggestionBadge } from '@/components/ai/SuggestionBadge';
-import { Building, ChevronDown, Menu, Zap, Bot, Layers, Code, Search } from 'lucide-react';
+import { Building, ChevronDown, Menu, Zap, Bot, Layers, Code, Search, ArrowLeft } from 'lucide-react';
 import { NotificationBell } from '@/components/layout/NotificationBell';
 import { WorkspaceSwitcher } from '@/components/layout/WorkspaceSwitcher';
 import { useWindowStore } from '@/store/windowStore';
@@ -69,6 +69,16 @@ export function TopBar() {
           <Menu className="w-4 h-4" aria-hidden="true" strokeWidth={2} />
         </button>
 
+        {/* Back to start arrow */}
+        <button
+          onClick={() => navigate('/start')}
+          className="p-2 rounded-md text-secondary-500 hover:bg-secondary-100 hover:text-secondary-700 min-h-touch min-w-touch flex items-center justify-center focus:outline-none focus-visible:ring-2 focus-visible:ring-primary-500"
+          aria-label="Zurück zur Startseite"
+          title="Zurück zur Startseite"
+        >
+          <ArrowLeft className="w-4 h-4" aria-hidden="true" strokeWidth={2} />
+        </button>
+
         {/* Tenant switcher */}
         {tenants && tenants.length > 0 && (
           <div className="relative">