feat: add SurveyInvite model

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

backend/alembic/env.py

@@ -14,6 +14,8 @@ from app.models.email_verification_token import EmailVerificationToken
 from app.models.tree_embedding import TreeEmbedding
 from app.models.copilot_conversation import CopilotConversation
 from app.models.assistant_chat import AssistantChat
+from app.models.survey_response import SurveyResponse
+from app.models.survey_invite import SurveyInvite
 from app.core.config import settings
 
 # this is the Alembic Config object