refactor: update AS entry handling in API and database to support ASN-only entries. Remove prefix field from AS entry structure and adjust related functions and tests. Enhance OpenAPI specifications and documentation to reflect changes in AS entry representation.

internal/httpapi/routes_crud.go

@@ -231,17 +231,7 @@ func (s *Server) handleListAS(w http.ResponseWriter, r *http.Request) {
 }
 
 func asEntryJSON(x *store.ASEntry) map[string]any {
-	m := map[string]any{"id": x.ID}
-	if x.ASN != nil {
-		m["asn"] = *x.ASN
-	} else {
-		m["asn"] = nil
-	}
-	if x.Prefix != nil {
-		m["prefix"] = *x.Prefix
-	} else {
-		m["prefix"] = nil
-	}
+	m := map[string]any{"id": x.ID, "asn": x.ASN}
 	if x.CommunityID != nil {
 		m["community_id"] = *x.CommunityID
 	} else {