feat: add SurveyInvite model

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -32,6 +32,8 @@ from .ai_chat_session import AIChatSession
 from .tree_embedding import TreeEmbedding
 from .copilot_conversation import CopilotConversation
 from .assistant_chat import AssistantChat
+from .survey_response import SurveyResponse
+from .survey_invite import SurveyInvite
 
 __all__ = [
     "User",
@@ -75,4 +77,6 @@ __all__ = [
     "TreeEmbedding",
     "CopilotConversation",
     "AssistantChat",
+    "SurveyResponse",
+    "SurveyInvite",
 ]