Added comprehensive BDD feature file and step definitions for user authentication
following ADR-0018. All tests are failing as expected per TDD practice.
- Created features/user_authentication.feature with 7 scenarios
- Added 17 step definitions for authentication flows
- Tests cover: user auth, admin auth, registration, password reset
- All tests fail with descriptive error messages
Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>