feat: Persist checkbox states in localStorage to retain settings after page reload

- Implemented logic to save the visibility states of POI and map layers in localStorage.
- Loaded saved checkbox states on component mount to retain user preferences.
- Updated `handleCheckboxChange` and `handlePoiCheckboxChange` to store changes in localStorage.
- Ensured that settings persist across page reloads for a better user experience.

hooks/useLineData.js

@@ -16,6 +16,8 @@ const useLineData = (webserviceGisLinesStatusUrl, setLineStatusData) => {
 
     ws.onopen = () => {
       console.log("WebSocket-Verbindung hergestellt");
+      // Testnachricht an den Server senden
+      ws.send(JSON.stringify({ type: "test", message: "Hallo vom Client" }));
     };
 
     ws.onmessage = (event) => {