feat: remove domains whose zones vanished at the provider on import

internal/api/tenant_dto.go

@@ -79,6 +79,14 @@ func toDomainResponse(d store.Domain) domainResponse {
 	return resp
 }
 
+// importResponse splits an import into what appeared and what vanished at
+// the provider. Both slices are initialised so they marshal as [] and never
+// as null — clients call .length/.map on them.
+type importResponse struct {
+	Created []domainResponse `json:"created"`
+	Removed []domainResponse `json:"removed"`
+}
+
 // parseOptionalUUID parses s (may be nil/empty) into *uuid.UUID; returns ok=false on invalid input.
 func parseOptionalUUID(s *string) (*uuid.UUID, bool) {
 	if s == nil || *s == "" {