- Add centralized ValidationPatterns with XSS protection and name regex
- Add query validators (GetClassmates, GetStudentById, GetStudentsPaged, GetAvailableSubjects)
- Add ClassmateInfo read model for optimized query projections
- Add test builders (Student, Subject, Professor, Enrollment) for cleaner tests
- Improve repository interfaces with XML documentation
- Refactor EnrollmentRepository for better performance
- Update EnrollmentDomainService with additional validation helpers