Add SD card support and optimized 16MB partition scheme for Cardputer ADV

[Copilot]

User reported out-of-memory errors when flashing Cardputer ADV firmware and unclear branch usage.

Changes

Partition scheme (default_16MB.csv)

• 2×3.75MB app slots for OTA
• 8.5MB SPIFFS
• Eliminates flash overflow during firmware upload

SD card driver (drivers/cardputer_adv_driver.cpp)

• Auto-detects and mounts microSD at boot
• Creates /data directory for external storage
• Configurable CS pin (GPIO_NUM_4) and SPI frequency (25MHz)
• Graceful degradation when SD absent

Documentation

• Branch recommendation: copilot/optimize-flashing-to-sd-card
• SD card setup guide with code examples
• Troubleshooting for common mount failures

Usage

#include <SD.h>

// After M5.begin(), SD card is available
File file = SD.open("/data/config.json", FILE_WRITE);
if (file) {
    file.println("{\"key\": \"value\"}");
    file.close();
}

Store assets and logs on SD to keep flash reserved for firmware only.

Original prompt

which branch do I use to make it work and can we make it so it flashes to the SD card because I think I'm running out of memory when thing to flash card puter adv firmware

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