fix: preserve existing URL parameters

mapper/src/App.js

@@ -559,7 +559,7 @@ function App() {
 
 	useEffect(() => {
 		const handler = setTimeout(() => {
-			const params = new URLSearchParams();
+			const params = new URLSearchParams(window.location.search);
 			params.set('duration', duration.id);
 			params.set('end', end.unix());
 			params.set('slider', slider.join(','));