Update STM32 MT6835 encoder bring-up

[snehaashahh]

Summary

• Add MT6835 encoder bring-up code that prints angle, raw readings, and status flags.
• Configure SPI chip select, enable encoder CRC checking, and avoid waiting indefinitely for Serial.
• Update STM32 PlatformIO settings for the Arduino app environment and ST-LINK serial monitor output.

Validation

• Not run locally in this session.

Notes

• This PR is based on WATonomous/humanoid:main and contains the two files from the screenshot: embedded/STM32/app/src/foc.cpp and embedded/STM32/platformio.ini.