feat(ui): move back arrow from topbar to sidebar header on all pages

frontend/src/pages/Settings.tsx

@@ -3,7 +3,7 @@ import { NavLink, Outlet } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { usePluginStore } from '@/store/pluginStore';
 import { useUIStore } from '@/store/uiStore';
-import { Settings, Mail, Bell, Sparkles, Bot, Shield, Users, UsersRound, Package } from 'lucide-react';
+import { Settings, Mail, Bell, Sparkles, Bot, Shield, Users, UsersRound, Package, ArrowLeft } from 'lucide-react';
 
 const ICON_MAP: Record<string, React.ComponentType<{ className?: string }>> = {
   Settings,
@@ -64,7 +64,17 @@ export function SettingsPage() {
     <div className="flex h-full overflow-hidden" data-testid="settings-page">
       <aside className={`${sidebarOpen ? 'w-64 border-r border-secondary-200' : 'w-0'} flex-shrink-0 min-h-[calc(100vh-4rem)] transition-all duration-200 overflow-hidden`}>
         <div className="w-64 flex-shrink-0 p-4">
-        <h1 className="text-xl font-bold text-secondary-900 mb-6">{t('settings.title')}</h1>
+          <div className="flex items-center gap-2 mb-6">
+            <button
+              onClick={() => window.location.href = '/start'}
+              className="p-1.5 rounded-md text-secondary-400 hover:bg-secondary-100 hover:text-secondary-700 flex items-center justify-center focus:outline-none"
+              aria-label="Zurück zur Startseite"
+              title="Zurück zur Startseite"
+            >
+              <ArrowLeft className="w-4 h-4" />
+            </button>
+            <h1 className="text-xl font-bold text-secondary-900">{t('settings.title')}</h1>
+          </div>
         <nav className="space-y-1" role="navigation" aria-label={t('settings.title')}>
           {navItems.map((item) => (
             <NavLink