Add also-notify support for BIND domains.conf generation

Extend catz.yaml config with a bind-conf section mapping catalog names
to also-notify IP lists. Zones in catalogs with also-notify configured
get an also-notify directive in the generated domains.conf. IPs are
deduplicated and sorted when a zone belongs to multiple catalogs.

bindconf.go

@@ -10,7 +10,8 @@ import (
 // generateBindConf produces a BIND domains.conf from all zone entries.
 // Zones are sorted alphabetically. Each zone block uses 8-space indentation.
 // DNSSEC zones get dnssec-policy and inline-signing directives on the file line.
-func generateBindConf(entries []ZoneEntry) string {
+// Zones in catalogs with also-notify configured get an also-notify directive.
+func generateBindConf(entries []ZoneEntry, cfg *Config) string {
 	sorted := make([]ZoneEntry, len(entries))
 	copy(sorted, entries)
 	sort.Slice(sorted, func(i, j int) bool {
@@ -38,16 +39,48 @@ func generateBindConf(entries []ZoneEntry) string {
 			fileLine += " dnssec-policy standard; inline-signing yes;"
 		}
 		b.WriteString(fileLine + "\n")
+
+		// Collect also-notify IPs from all catalogs this zone belongs to
+		ips := alsoNotifyIPs(entry.Catalogs, cfg)
+		if len(ips) > 0 {
+			b.WriteString("        also-notify {")
+			for _, ip := range ips {
+				fmt.Fprintf(&b, " %s;", ip)
+			}
+			b.WriteString(" };\n")
+		}
+
 		b.WriteString("};\n")
 	}
 
 	return b.String()
 }
 
+// alsoNotifyIPs returns the deduplicated, sorted list of also-notify IPs
+// for a zone based on its catalog memberships.
+func alsoNotifyIPs(catalogs []string, cfg *Config) []string {
+	if len(cfg.BindConf.AlsoNotify) == 0 {
+		return nil
+	}
+
+	seen := make(map[string]bool)
+	var ips []string
+	for _, catName := range catalogs {
+		for _, ip := range cfg.BindConf.AlsoNotify[catName] {
+			if !seen[ip] {
+				seen[ip] = true
+				ips = append(ips, ip)
+			}
+		}
+	}
+	sort.Strings(ips)
+	return ips
+}
+
 // writeBindConf writes the BIND config to path.
 // Zones without a ZoneFile are skipped (catalog-only zones).
-func writeBindConf(path string, entries []ZoneEntry) error {
-	content := generateBindConf(entries)
+func writeBindConf(path string, entries []ZoneEntry, cfg *Config) error {
+	content := generateBindConf(entries, cfg)
 	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
 		return fmt.Errorf("writing bind config %s: %w", path, err)
 	}