- increase UART DMA/ring buffer sizes for mux traffic
- switch SPI1 to Mode0 with prescaler /2 and align CubeMX settings
- refactor CH390 memory read/write path with chunked SPI read and HAL bulk write
- fallback to hardware MAC when configured MAC is invalid (all-zero)
- add mux frame RTT logs and remove redundant UART1 polling
- update Keil post-build viewer integration and include build viewer artifacts
- update AT manual with all-zero MAC behavior
