Add extended forward zone type for overriding public domain records

An extended zone answers authoritatively only for the records it holds
locally; any name with nothing configured falls through to recursive
resolution instead of a synthesized NXDOMAIN, so a public domain's
records don't need to be duplicated just to override a few of them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V8c76Xr2BycaHHu5N4buqi

internal/database/store_zones.go

@@ -33,7 +33,7 @@ func scanZone(sc interface{ Scan(...any) error }) (models.Zone, error) {
 
 // ZoneFilter narrows a zone listing.
 type ZoneFilter struct {
-	Kind   string // "", "forward", "reverse4", "reverse6", or "reverse" for both
+	Kind   string // "", "forward" (includes extended), "extended", "reverse4", "reverse6", or "reverse" for both reverse kinds
 	Search string
 }
 
@@ -47,6 +47,8 @@ func (db *DB) Zones(ctx context.Context, f ZoneFilter) ([]models.Zone, error) {
 		// no filter
 	case "reverse":
 		where = append(where, "z.kind IN ('reverse4','reverse6')")
+	case "forward":
+		where = append(where, "z.kind IN ('forward','extended')")
 	default:
 		where = append(where, "z.kind = ?")
 		args = append(args, f.Kind)