feat(UI-Overhaul-Phase2): AI Assistent in Kommunikation integriert

Migration 0137: Drop AI chat tables (ai_chat_sessions, ai_chat_messages, ai_chat_attachments, ai_conversations, ai_messages)

Backend:
- Remove AIChatSession, AIChatMessage, AIChatAttachment models from ai_assistant/models.py
- Remove AIConversation, AIMessage from app/models/__init__.py
- Remove session/message/stream/attachment routes from ai_assistant/routes.py
- Add new streaming route POST /ai/conversations/{conversation_id}/stream using comm tables
- Add new messages route GET /ai/conversations/{conversation_id}/messages using comm tables
- Add stream_chat_comm, get_comm_messages, save_comm_message to services.py
- Update external_api.py to use CommConversation/CommMessage instead of AIChatSession/AIChatMessage
- Update unified_search ai_chat_provider to search comm_messages with conversation_type=ai
- Remove ai_copilot router from main.py and routes/__init__.py
- Remove ai_conversation from entity_permissions.py and owner_transfer_service.py
- Update ai_assistant/plugin.py get_entity_models to remove AIChatSession
- Guard ai_copilot_service.py imports with try/except

Frontend:
- Remove AIAssistant.tsx, AIAssistantStandalone.tsx, SessionList.tsx, ChatWindow.tsx
- Remove AI Assistant routes from routes/index.tsx
- Update api/ai.ts: streamChat uses /ai/conversations/{id}/stream, fetchMessages uses /ai/conversations/{id}/messages
- Update Communication.tsx: use convId for AI streaming, remove aiSessionId, use fetchAiMessages for AI conversations
- Update AiChatPanel.tsx: create comm conversation instead of AI session, use new fetchMessages
- Update AISidebar.tsx: remove ChatWindow import, show placeholder

tsc clean, build successful, backend import OK

frontend/src/pages/Communication.tsx

@@ -11,7 +11,7 @@ import {
 import { ResizablePanel } from '@/components/ui/ResizablePanel';
 import { usePluginToolbarStore } from '@/store/pluginToolbarStore';
 import { apiClient } from '@/api/client';
-import { streamChat, fetchAgents, type AIAgent } from '@/api/ai';
+import { streamChat, fetchAgents, fetchMessages as fetchAiMessages, type AIAgent } from '@/api/ai';
 
 // ─── Types ───
 
@@ -322,7 +322,6 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
   const [miniApps, setMiniApps] = useState<MiniApp[]>([]);
   const [agents, setAgents] = useState<AIAgent[]>([]);
   const [selectedAgentId, setSelectedAgentId] = useState<string | null>(null);
-  const [aiSessionId, setAiSessionId] = useState<string | null>(null);
   const scrollRef = useRef<HTMLDivElement>(null);
   const wsRef = useRef<WebSocket | null>(null);
 
@@ -331,11 +330,38 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
     if (!convId) return;
     setLoading(true);
     setError(null);
-    fetchMessages(convId)
-      .then(msgs => { setMessages(msgs); setLoading(false); })
-      .catch(e => { setError(e?.message || 'Fehler beim Laden'); setLoading(false); });
+    if (category === 'ai') {
+      // AI conversations load messages from the AI endpoint
+      fetchAiMessages(convId)
+        .then(msgs => {
+          // Convert {role, content}[] to Message[] format
+          const mapped: Message[] = msgs.map((m, i) => ({
+            id: `ai-msg-${i}`,
+            conversation_id: convId,
+            sender_id: null,
+            sender_type: m.role === 'user' ? 'user' : 'ai',
+            content: m.content,
+            content_format: 'text',
+            created_at: null,
+            edited_at: null,
+            is_pinned: false,
+            blocks: [],
+            attachments: [],
+            reactions: [],
+            reply_to_id: null,
+          }));
+          setMessages(mapped);
+          setLoading(false);
+        })
+        .catch(e => { setError(e?.message || 'Fehler beim Laden'); setLoading(false); });
+    } else {
+      // Regular conversations load from comm endpoint
+      fetchMessages(convId)
+        .then(msgs => { setMessages(msgs as unknown as Message[]); setLoading(false); })
+        .catch(e => { setError(e?.message || 'Fehler beim Laden'); setLoading(false); });
+    }
     markConversationRead(convId).catch(() => {});
-  }, [convId]);
+  }, [convId, category]);
 
   // Load agents and mini-apps
   useEffect(() => {
@@ -386,12 +412,12 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
     setError(null);
 
     try {
-      if (category === 'ai' && aiSessionId) {
-        // AI streaming chat
+      if (category === 'ai') {
+        // AI streaming chat via comm conversation
         setAiStreaming(true);
         setStreamingContent('');
         let accumulated = '';
-        for await (const event of streamChat(aiSessionId, content, selectedAgentId || undefined)) {
+        for await (const event of streamChat(convId, content, selectedAgentId || undefined)) {
           if (event.type === 'token' && event.content) {
             accumulated += event.content;
             setStreamingContent(accumulated);
@@ -405,8 +431,23 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
         setAiStreaming(false);
         setStreamingContent('');
         // Reload messages to get the AI response
-        const msgs = await fetchMessages(convId);
-        setMessages(msgs);
+        const msgs = await fetchAiMessages(convId);
+        const mapped: Message[] = msgs.map((m, i) => ({
+          id: `ai-msg-${i}`,
+          conversation_id: convId,
+          sender_id: null,
+          sender_type: m.role === 'user' ? 'user' : 'ai',
+          content: m.content,
+          content_format: 'text',
+          created_at: null,
+          edited_at: null,
+          is_pinned: false,
+          blocks: [],
+          attachments: [],
+          reactions: [],
+          reply_to_id: null,
+        }));
+        setMessages(mapped);
       } else {
         // Regular message
         const msg = await sendMessage(convId, content);
@@ -426,25 +467,10 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
     }
   };
 
-  const startAiSession = async () => {
-    try {
-      const r = await apiClient.post('/ai/sessions', {
-        title: 'KI Chat',
-        agent_id: selectedAgentId,
-        is_sidebar: false,
-      });
-      setAiSessionId(r.data.id);
-    } catch (e: unknown) { const errObj = asError(e);
-      setError('KI Session konnte nicht gestartet werden');
-    }
-  };
-
-  // Auto-start AI session for AI conversations
+  // Auto-scroll
   useEffect(() => {
-    if (category === 'ai' && !aiSessionId && selectedAgentId) {
-      startAiSession();
-    }
-  }, [category, aiSessionId, selectedAgentId]);
+    if (scrollRef.current) scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
+  }, [messages, streamingContent]);
 
   return (
     <div className="flex flex-col h-full bg-white">
@@ -462,7 +488,7 @@ function ChatWindow({ convId, category, onBack }: ChatWindowProps) {
         {category === 'ai' && agents.length > 0 && (
           <select
             value={selectedAgentId || ''}
-            onChange={(e) => { setSelectedAgentId(e.target.value || null); setAiSessionId(null); }}
+            onChange={(e) => { setSelectedAgentId(e.target.value || null); }}
             className="text-xs border border-secondary-200 rounded px-2 py-1 bg-white"
           >
             {agents.map(a => (