docs: fix AEP MultiZone link

[tharune]

Summary

• replace AEP-12's stale Hex Five MultiZone product URL with the active MultiZone IoT SDK repository for RISC-V

Verification

• confirmed https://hex-five.com/multizone-security-sdk/ returns 404
• confirmed https://github.com/hex-five/multizone-iot-sdk returns 200 and describes MultiZone for RISC-V processors
• ran git diff --check

[tharune]

Closing this wrong-repo AEP mirror PR per maintainer guidance. Recreated against the source AEP repo here: akash-network/AEP#107