feat(ch390): optimize SPI transfer, MAC fallback, and build settings for V1.0.0

- 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

Core/Src/spi.c

@@ -44,7 +44,7 @@ void MX_SPI1_Init(void)
   hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;    /* Match CH390 runtime baseline: CPOL=Low */
   hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;        /* Match CH390 runtime baseline: CPHA=1Edge (Mode 0) */
   hspi1.Init.NSS = SPI_NSS_SOFT;                /* Software CS control for CH390 */
-  hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_64; /* 72MHz/64 = 1.125MHz for conservative CH390 bring-up */
+  hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_2; /* 72MHz/2 = 36MHz, max SPI1 clock at current APB2 */
   hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
   hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
   hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;