Adds a built-in preset for the Polish MeshCore community broker at
mqtt.marwoj.net: MQTT over TLS on port 8883, username/password auth
with credentials embedded in firmware, and the standard MeshCore topic
layout. The Let's Encrypt chain anchors at the existing ISRG_ROOT_X1
constant, so no new CA certificate is needed.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>