The C6 autodetect picked the CUSTOM profile, but load_board_profile() has
no entry for it, so Rx, Tx and the button stayed at the placeholder 99.
The startup settings load then failed the GPIO check and fell back to an
empty settings object (blank Board Profile, Tx Mode and Bus ID), and every
Application settings save returned 400 until valid pins were sent together
with CUSTOM through the API.
Start a C6 without a profile as CUSTOM with pins for the Seeed XIAO
ESP32-C6 (the c6_xiao_4M build): Rx GPIO20 (D9), Tx GPIO19 (D8), button
GPIO9 (BOOT), no LED, no Dallas sensor.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
