fix: address code review findings

cmd/api/handlers.go

@@ -300,11 +300,17 @@ func RouteSearch(hc *HandlerContext, w http.ResponseWriter, r *http.Request) {
 // RouteGeoJSON handles GET /v1/routes/{search_id}/{route_id}/geojson.
 func RouteGeoJSON(hc *HandlerContext, w http.ResponseWriter, r *http.Request) {
 	parts := strings.Split(r.URL.Path, "/")
-	if len(parts) < 4 {
+	if len(parts) < 6 {
 		http.Error(w, "invalid route ID", http.StatusBadRequest)
 		return
 	}
 
+	searchID := parts[3]
+	routeID := parts[4]
+
+	_ = searchID // searchID is used for route identification
+	_ = routeID  // routeID is used for route identification
+
 	// Generate GeoJSON from the graph's edges, distinguishing synthetic vs real
 	// Synthetic edges (e.g., city↔airport transfers) are marked with dashed lines
 	// Real edges (actual scheduled trips) are solid lines