HomeMate PKI trust endpoint.

Public CA artifacts:
  /ca-bundle.pem              — root + intermediate (recommended for device firmware)
  /homemate-root-ca.crt       — root only
  /homemate-issuing-ca.crt    — intermediate only

The MQTT broker at mqtts://mqtt.homematesmart.com:8884 presents a cert
chained to these CAs. Bake /ca-bundle.pem into device firmware to verify it.