feat: treeview with folders, toolbar, file attachments in chat

frontend/src/pages/AIAssistant.tsx

@@ -1,13 +1,43 @@
-import React, { useState } from 'react';
+import React, { useState, useEffect } from 'react';
 import { SessionList } from '@/components/ai/SessionList';
 import { ChatWindow } from '@/components/ai/ChatWindow';
+import { usePluginToolbarStore } from '@/store/pluginToolbarStore';
+import { fetchAgents, type AIAgent } from '@/api/ai';
 
 export function AIAssistantPage() {
   const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
+  const [agents, setAgents] = useState<AIAgent[]>([]);
+  const [selectedAgentId, setSelectedAgentId] = useState<string | null>(null);
+  const { registerItems, unregisterPlugin } = usePluginToolbarStore();
+
+  useEffect(() => {
+    fetchAgents().then(setAgents).catch(() => {});
+  }, []);
+
+  useEffect(() => {
+    registerItems('ai_assistant', [
+      {
+        id: 'agent-select',
+        label: 'Agent',
+        type: 'select',
+        options: agents.map((a) => ({ value: a.id, label: a.name })),
+        value: selectedAgentId || '',
+        onChange: (val: string) => setSelectedAgentId(val || null),
+      },
+      {
+        id: 'new-chat',
+        label: 'Neuer Chat',
+        type: 'button',
+        onClick: () => setActiveSessionId(null),
+      },
+    ]);
+
+    return () => unregisterPlugin('ai_assistant');
+  }, [agents, selectedAgentId, registerItems, unregisterPlugin]);
 
   return (
     <div className="flex h-full" data-testid="ai-assistant-page">
-      {/* Left: Session List */}
+      {/* Left: Session List with TreeView */}
       <div className="w-72 flex-shrink-0 border-r border-secondary-200 bg-white">
         <div className="h-16 flex items-center px-6 border-b border-secondary-200">
           <h1 className="text-lg font-bold text-secondary-900">KI Assistent</h1>
@@ -21,7 +51,7 @@ export function AIAssistantPage() {
       {/* Right: Chat Window */}
       <div className="flex-1 flex flex-col">
         {activeSessionId ? (
-          <ChatWindow sessionId={activeSessionId} className="flex-1" />
+          <ChatWindow sessionId={activeSessionId} agentId={selectedAgentId} className="flex-1" />
         ) : (
           <div className="flex-1 flex items-center justify-center text-secondary-400">
             <div className="text-center">