feat: Add comprehensive unit tests for LoginHelperService

- Created LoginHelperServiceTest with 15 tests covering critical authentication flow
  - Tests last activity date tracking on login
  - Tests automatic user unlocking after lockout duration
  - Tests DSUserDetails creation with proper authorities
  - Tests handling of locked, disabled, and OAuth2 users
  - Tests role and privilege assignment
  - Tests edge cases like null dates and rapid successive logins

- All tests verify real business logic, not just mock interactions
- Tests provide valuable coverage for authentication helper operations
- Ensures proper integration with LoginAttemptService and AuthorityService

Test count increased from 251 to 266 (15 new tests)
All tests passing with 100% success rate

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: devondragon