Support native SD storage and consolidate fds-flash tooling

Accept native SD cards for internal settings alongside legacy NVMe,
reject USB ancestry and ambiguous disks, and preserve read-only boot
loading with explicit recovery writes. Require built-in MMC drivers,
validate cached kernel configuration, and provide SD-only, SD-first and
USB-first EEPROM profiles.

Expose typed create and inspect commands through fds-flash, reuse the
existing cartridge creation code, and document the optional e2fsprogs
package dependency. Extend storage, EEPROM, flashing and hardware-test
coverage and advance the wiki reference to the published SD guide.

Validation: rootfs checks for CLI/development, boot matrix, internal
storage, EEPROM, flash, workstation, emulator, make check and wiki checks
passed. The full internal suite passed on an unchanged rerun after one
unexplained VM shutdown stall. Standalone init-test was blocked by its
unavailable pinned upstream kernel. Physical Pi checks remain pending.

image/build-internal

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Create a complete internal NVMe GPT image as a new ordinary file."""
+"""Create a complete internal SD/NVMe GPT image as a new ordinary file."""
 import argparse
 import json
 import os
@@ -93,5 +93,5 @@ if args.output_directory is None:
     link = project / 'out/fds-internal.img.next'
     link.symlink_to(work.name + '/internal.img')
     link.replace(project / 'out/fds-internal.img')
-print(f'PASS: complete internal NVMe image, three verified GPT payloads: {work}')
-print('SKIP: no physical disk was written; Pi firmware/NVMe boot requires hardware')
+print(f'PASS: complete internal SD/NVMe image, three verified GPT payloads: {work}')
+print('SKIP: no physical disk was written; Pi firmware/SD boot requires hardware')