feat: implement stale client removal after timeout

- add goroutine to remove stale clients from the connection pool
- update client struct to track `LastPong` time
- set write deadline for websocket connections
- move package variables and const to `vars.go`
- log additional information when broadcasting errors

🤖

internal/websocket/client_commands.go

@@ -21,6 +21,7 @@ func handleClientCommands(c models.WebsocketClient) {
 
 		_, message, err := ws.ReadMessage()
 		if err != nil {
+			// remove client on error/disconnect
 			delete(Clients, ws.LocalAddr())
 			helper.Logger.Info("Client disconnected:", "msg", err, "host", c.RealIP, "clients", len(Clients))
 			break