Fix coin tracker data persistence issue

- Updated API URLs from localhost:3000 to localhost:3001 in script.js
- Added CORS headers to server.js to enable cross-origin requests
- Changed server port from 3000 to 3001 to avoid port conflicts
- Updated CSP in index.html to allow connections to localhost:3001
- Coin tracker entries now persist across page refreshes

html/rechner/index.html

@@ -8,7 +8,7 @@
     script-src 'self' 'unsafe-inline' 'unsafe-eval' https://cdn.jsdelivr.net;
     style-src 'self' 'unsafe-inline';
     img-src 'self' data:;
-    connect-src 'self' http://localhost:3000;
+    connect-src 'self' http://localhost:3001;
   ">
   <title>Rechner</title>