feat: add fixed questions and improve authentication

.gitignore

@@ -93,6 +93,8 @@ offline-backend-20260512/backend/tests/*
 # Keep the model configuration regression coverage versioned even though
 # this deployment repository otherwise ignores newly added backend tests.
 !offline-backend-20260512/backend/tests/test_model_management.py
+# Keep fixed-question exact-match and streaming regression coverage versioned.
+!offline-backend-20260512/backend/tests/test_fixed_questions.py
 deploy
 .history