[FuTseYi]

Changes

• Validate Intel HEX record framing, length, checksums, known record types and terminal EOF for firmware/prebuilt/Template.hex; print SHA-256 for reproducibility.
• Extend the Keil CI job to run the HEX integrity checker after verifying project paths.
• Add docs/FIRMWARE-VERIFICATION.md detailing Keil native rebuild steps, hardware acceptance work and distinctions between integrity checks and actual hardware verification.
• Link the verification instructions from English/Chinese READMEs.

Safety and limitations

• This PR does not modify STM32 application C code, Keil project file or existing HEX image.
• Passing integrity checks does not establish compatibility with particular hardware, sensor accuracy or regulatory fitness.