feat: add standalone AI assistant window button

- Add ExternalLink button to AI assistant toolbar
- New route /ai-assistant-standalone renders AIAssistantPage without sidebar
- Opens in new browser window via window.open

frontend/src/pages/AIAssistant.tsx

@@ -4,7 +4,7 @@ import { ChatWindow } from '@/components/ai/ChatWindow';
 import { ResizablePanel } from '@/components/ui/ResizablePanel';
 import { usePluginToolbarStore } from '@/store/pluginToolbarStore';
 import { fetchAgents, createSession, type AIAgent } from '@/api/ai';
-import { ChevronLeft, Folder, Plus } from 'lucide-react';
+import { ChevronLeft, ExternalLink, Folder, Plus } from 'lucide-react';
 
 export function AIAssistantPage() {
   const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
@@ -67,6 +67,19 @@ export function AIAssistantPage() {
           }
         },
       },
+      {
+        id: 'open-standalone',
+        plugin: 'ai_assistant',
+        label: 'In neuem Fenster',
+        type: 'button',
+        group: 'actions',
+        icon: (
+          <ExternalLink className="w-3.5 h-3.5" strokeWidth={2} />
+        ),
+        onClick: () => {
+          window.open('/ai-assistant-standalone', '_blank', 'width=800,height=600');
+        },
+      },
     ]);
     return () => unregisterPlugin('ai_assistant');
   }, [agents, selectedAgentId, registerItems, unregisterPlugin]);

frontend/src/pages/AIAssistantStandalone.tsx

@@ -0,0 +1,10 @@
+import React from 'react';
+import { AIAssistantPage } from './AIAssistant';
+
+export function AIAssistantStandalonePage() {
+  return (
+    <div className="h-screen w-screen overflow-hidden bg-white">
+      <AIAssistantPage />
+    </div>
+  );
+}

frontend/src/routes/index.tsx

@@ -36,6 +36,7 @@ const AISettingsPage = React.lazy(() => import('@/pages/AISettings').then(m => (
 const ProactiveAISettings = React.lazy(() => import('@/pages/ProactiveAISettings').then(m => ({ default: m.ProactiveAISettings })));
 const SettingsThemePage = React.lazy(() => import('@/pages/SettingsTheme').then(m => ({ default: m.SettingsThemePage })));
 const SettingsMcpPage = React.lazy(() => import('@/pages/SettingsMcp').then(m => ({ default: m.SettingsMcpPage })));
+const AIAssistantStandalonePage = React.lazy(() => import('@/pages/AIAssistantStandalone').then(m => ({ default: m.AIAssistantStandalonePage })));
 const SettingsAIPage = React.lazy(() => import('@/pages/SettingsAI').then(m => ({ default: m.SettingsAIPage })));
 const SettingsMenuOrderPage = React.lazy(() => import('@/pages/SettingsMenuOrder').then(m => ({ default: m.SettingsMenuOrderPage })));
 const SettingsStammdatenPage = React.lazy(() => import('@/pages/SettingsStammdaten').then(m => ({ default: m.SettingsStammdatenPage })));
@@ -65,6 +66,10 @@ const router = createBrowserRouter([
     path: '/login',
     element: <LoginPage />,
   },
+  {
+    path: '/ai-assistant-standalone',
+    element: withSuspense(<AIAssistantStandalonePage />),
+  },
   {
     path: '/password-reset',
     element: <PasswordResetRequestPage />,