[web] Support libevent as WS server instead of libwebsockets

If libevent >= 2.2 is detected during configure and "websocket_port" == 0 in the config file, the libwebsocket implementation is disabled and instead the libevent http server offers the websocket connection. The connection to the websocket is then done with the path "/ws".

web-src/vite.config.js

@@ -39,6 +39,7 @@ export default defineConfig({
   server: {
     proxy: {
       '/api': { target },
+      '/ws': { target: target, ws: true },
       '/artwork': { target },
       '/stream.mp3': { target }
     }