M5 support preview 1 — F21 / M5 Bands

Adds automatic F21 Pro / Tiq M5 detection and M5 EU ↔ USA band swapping, using the existing F21 backup, eMMC unlock, streaming dd, flush, and reboot flow. M5 and F21 bundles and backups are kept separate.

Includes the F21 custom-ROM detection regression fix. M5 requires active slot _a and the existing Magisk su / su -mm root flow. The ADB-only privileged shell is not integrated.

Validation: APK build and signature verification passed; model detection, region selection, bundle isolation, malformed archive, and F21 compatibility tests passed. Both published M5 bundles were downloaded and verified against local hashes.

Experimental: live flashing with this APK has not been tested on M5. The USA modem image is zero-padded to the measured 100 MiB partition capacity. A successful build and matching partition layout do not establish hardware flashing safety.