Group UART sensors into channel slots and add an MS board overlay
with per-port speed and sensor mode configuration. Also add optional
per-second channel diagnostic output controlled by APP_DEBUG_PRINT.
- Add CONFIG_SAMPLE_NTC to CMakeLists.txt and Kconfig
- Implement PI temperature controller with PWM output in heating.hpp
- Convert NtcGroup from template to non-template class
- Add LED helper class with flash support
- Implement COM protocol handlers for device ID and running state
- Add SPI, sensor, and PWM configuration to prj.conf
- Remove indicator overlay and update main.cpp with temperature
monitoring
- Add test script for serial protocol communication
