fix: parse npm 12 pack metadata

[bntvllnt]

Summary

• parse both npm 11 array-shaped and npm 12 package-keyed npm pack --json output
• extract and validate filename plus integrity in one fail-closed parser
• apply the parser to canary and stable publication paths

Context

The second canary attempt reached npm 12 successfully, then failed because npm 12 changed npm pack --json from an array to an object keyed by package name.

Verification

• exact npm 12.0.2 output parsed successfully
• tarball filename exists and integrity is populated
• pnpm format:check
• git diff --check

No stable package is published or tagged by this PR.

[greptile-apps]

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