Fix TestMessage import in verification_store.py

- Add missing TestMessage import from verification_models
- Resolves NameError: name 'TestMessage' is not defined
- Completes import fixes for Hugging Face Spaces deployment

src/core/verification_store.py

@@ -20,6 +20,7 @@ from src.core.verification_models import (
     VerificationSession,
     VerificationRecord,
     TestDataset,
+    TestMessage,
     EnhancedVerificationSession,
     TestCaseEdit,
     FileUploadResult,