Changed hardcoded MQTT_BROKER_URL to read from .env file with fallback to mqtt://mosquitto:1883. This allows using external MQTT brokers like mqtt://tracking.unixweb.de:1883 by simply updating the .env file.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>