[minor] Validate formula release assets

[libops-agent]

Summary

• add unprivileged pull-request validation for Homebrew formulas
• require non-empty descriptions, MIT licensing, exact LibOps release URLs, and adjacent SHA-256 values
• download every changed formula asset and verify its declared digest
• reject accidental formula deletion and test the verifier itself

Validation

• actionlint v1.7.12
• GitHub-hosted Ruby tests (Ruby is not installed in the workspace)
• git diff --check