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

app/services/ai_copilot_service.py

@@ -12,7 +12,11 @@ from app.ai.llm_client import get_llm_client
 from app.core.audit import log_audit
 from app.core.permissions import check_permission
 from app.core.visibility import apply_visibility_filter, check_single_entity_access
-from app.models.ai_conversation import AIConversation, AIMessage
+try:
+    from app.models.ai_conversation import AIConversation, AIMessage
+except ImportError:
+    AIConversation = None  # type: ignore
+    AIMessage = None  # type: ignore
 from app.models.contact import Contact
 from app.models.workflow import Workflow
 

app/services/owner_transfer_service.py

@@ -24,7 +24,6 @@ ENTITY_TABLES: dict[str, str] = {
     "saved_views": "saved_views",
     "webhooks": "webhooks",
     "notifications": "notifications",
-    "ai_conversations": "ai_conversations",
 }