Add doc:/readOnly:/writeOnly: tags to the shared LinkSharing model so the
Huma-generated /api/v2 schema documents every exposed field. password is
write-only (set on create, never returned); hash, sharing_type, id,
created, updated and shared_by are server-controlled and marked read-only.
swaggo/XORM/govalidator ignore these tags, so v1 is unaffected.