- Introduced package-level error variables in registry to replace repeated fmt.Errorf calls - Added errors like ErrSessionNotFound, ErrSlugInUse, ErrInvalidSlug, ErrForbiddenSlug, ErrSlugChangeNotAllowed, and ErrSlugUnchanged
- Introduced package-level error variables in registry to replace repeated fmt.Errorf calls - Added errors like ErrSessionNotFound, ErrSlugInUse, ErrInvalidSlug, ErrForbiddenSlug, ErrSlugChangeNotAllowed, and ErrSlugUnchanged