FreeRTOS/Zephyr POSIX simulator CI/CD integration #9

Context

Add CI/CD coverage for the FreeRTOS/Zephyr POSIX simulator integration in this repository.

Goal

Keep the existing Zephyr build checks, and add a bounded runtime smoke check for the FreeRTOS POSIX simulator in GitHub Actions.

Scope

• FreeRTOS POSIX simulator runtime smoke in PR CI
• Same smoke gate in release workflow before publishing artifacts
• Zephyr remains build-only for this issue

Status

Implemented in PR #10.