feat: add secure-enclave EIF build and GHCR carrier image workflow

[kilianglas]

Summary

This PR adds the Nitro enclave EIF build for secure-enclave and publishes a carrier image.

Follows the enclave pattern used for the world-chain proof system: workload image → EIF + PCRs → carrier image.

[semgrep-code-worldcoin]

Semgrep identified an issue in your code:

Third-party action docker/metadata-action@v5 is referenced by mutable version tag instead of immutable commit SHA, allowing attackers who compromise the repository to inject malicious code into your workflow.

More details about this

The action docker/metadata-action@v5 is pinned to a version tag rather than a specific commit SHA. This means the tag reference (v5) can be updated or replaced at any time by the maintainers of the docker/metadata-action repository, potentially without your knowledge.

Here's a concrete attack scenario:

1. An attacker compromises the docker/metadata-action repository or tricks maintainers into merging malicious code.
2. They push a new commit and update the v5 tag to point to their compromised version (tags in Git are mutable by default).
3. Your workflow runs and pulls docker/metadata-action@v5, which now fetches the attacker's malicious code instead of the original.
4. The malicious action could extract secrets from the GitHub Actions environment (like ${{ secrets.GITHUB_TOKEN }}), steal repository data, or inject backdoors into your build artifacts.
5. Since your workflow uses this action to tag and push images to ghcr.io/${{ github.repository }}-enclave-eif, the attacker could now push a compromised container image to your registry.

Using a full commit SHA (like @a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b) instead of the tag makes the reference immutable—the specific code that runs is locked in and cannot be changed retroactively.

To resolve this comment:

✨ Commit fix suggestion

1. Replace the version tag in the uses line with the full 40-character commit SHA for docker/metadata-action instead of @v5.
2. Keep the current major version visible in a comment so the workflow stays readable, for example: uses: docker/metadata-action@<full-commit-sha> # v5.
3. Get the correct SHA from the docker/metadata-action repository release or tag that corresponds to v5, and pin exactly that commit. This makes the action reference immutable so the workflow cannot silently pick up different code later.

💬 Ignore this finding

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_{You can view more details about this finding in the Semgrep AppSec Platform.}

[semgrep-code-worldcoin]

Semgrep found 9 github-actions-mutable-action-tag findings:

• .github/workflows/build-enclave-eif.yml
  • L44 - Triage
  • L47 - Triage
  • L50 - Triage
  • L86 - Triage
  • L94 - Triage
  • L103 - Triage
  • L107 - Triage
  • L115 - Triage
  • L127 - Triage

GitHub Actions step uses a mutable tag or branch reference. Tags and branch names can be silently repointed by the action owner, enabling supply-chain attacks — as seen in the trivy-action and kics-github-action compromises. Pin the reference to a full 40-character commit SHA instead, e.g. uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608.