Allow catalog-only zones without file= in --bind-conf mode

Zones without a file= property (e.g. ddns zones) are included in
catalog zone output for secondaries but skipped in domains.conf.
Previously --bind-conf required every zone to have file= set.

bindconf.go

@@ -23,6 +23,10 @@ func generateBindConf(entries []ZoneEntry) string {
 	b.WriteString("#\n")
 
 	for _, entry := range sorted {
+		if entry.ZoneFile == "" {
+			continue // catalog-only zone, no BIND config needed
+		}
+
 		// Strip trailing dot for BIND zone name
 		zoneName := strings.TrimSuffix(entry.Zone, ".")
 
@@ -40,22 +44,9 @@ func generateBindConf(entries []ZoneEntry) string {
 	return b.String()
 }
 
-// validateBindConf checks that every zone entry has a non-empty ZoneFile.
-func validateBindConf(entries []ZoneEntry) error {
-	for _, entry := range entries {
-		if entry.ZoneFile == "" {
-			return fmt.Errorf("%s:%d: zone %s missing file= property (required for --bind-conf)",
-				entry.ZonesFile, entry.Line, entry.Zone)
-		}
-	}
-	return nil
-}
-
-// writeBindConf validates entries and writes the BIND config to path.
+// writeBindConf writes the BIND config to path.
+// Zones without a ZoneFile are skipped (catalog-only zones).
 func writeBindConf(path string, entries []ZoneEntry) error {
-	if err := validateBindConf(entries); err != nil {
-		return err
-	}
 	content := generateBindConf(entries)
 	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
 		return fmt.Errorf("writing bind config %s: %w", path, err)