Sort numeric labels by value

Records, zones and findings now order all-digit labels numerically, so
reverse zones list 2 before 101. model.CanonicalLess is replaced by
model.NameLess; other labels keep byte order.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/h_stats.go

@@ -215,7 +215,7 @@ func clientNames(st *model.State, want map[netip.Addr]bool, readable func(*model
 	}
 	slices.SortFunc(recs, func(a, b *model.Record) int {
 		if a.Name != b.Name {
-			if model.CanonicalLess(a.Name, b.Name) {
+			if model.NameLess(a.Name, b.Name) {
 				return -1
 			}
 			return 1