New docs/postmortems/ folder. The bench card (133 GB SDXC) rejects CMD59
(SPI-mode CRC) as illegal; CMD0/CMD8 succeed, so wiring and firmware are
proven and the fix is a compliant card. Captures the root cause, the
keep-CRC-required decision, and the reusable findings (EPD bus lock, LFN
requirement, R1-byte diagnostic) before the work pauses for hardware.
