The MQTT/WebSocket broker is back online

[br-g]

The MQTT/WebSocket broker experienced an issue during the last race and was unavailable for a few days. For context, see: #424

Everything should now be fully operational again.

I have made the following changes to improve reliability and stability:

• Improved the code that sends data to the MQTT/WebSocket broker so it handles disconnections more robustly: b1ad819
• Strengthened broker security and abuse prevention. In particular, connections are now limited to 10 per user. There was previously no connection limit, and the broker had recently been heavily abused, which contributed to instability.

Thanks for your patience while this was being fixed.