ci: require CodeRabbit review check for enhancement proposals

[minmzzhang]

Summary

Require the existing CodeRabbit status check for enhancement-proposals before merging.

The repository continues to require two human approvals. This adds automated review completion as a separate required status check; it does not count CodeRabbit as a human approval.

Test plan

• git diff --check
• Run tofu fmt -check
• Run tofu plan
• Confirm the applied ruleset requires CodeRabbit
• Confirm a PR with a failing or missing CodeRabbit check cannot merge

Assisted-by: Codex noreply@openai.com

[coderabbitai]

Important

Draft PR not reviewed

Draft PRs are not automatically reviewed by default.

• Trigger a manual review

To automatically review draft PRs, update your CodeRabbit configuration:

reviews:
  auto_review:
    drafts: true

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_{Comment @coderabbitai help to get the list of available commands.}

[minmzzhang]

Closing this draft because CodeRabbit should not be a required merge check.