- Add Handler struct with StartOnboarding, GetMVNO, and ListMVNOs methods in handler.go
- Add ManagementHandler struct with GetMVNO, ListMVNOs, UpdateMVNOStatus, and GetMVNOStats methods in handler_management.go
- Add RegisterRoutes method for /mvno/onboarding, /mvno, and /mvno/:id route registration
- Add query parameter parsing for status, plan, and limit filters in ListMVNOs
- Add structured logging with mvno_id, status, and error
