Add optional Homebrew Cask PR creation to production releases

[NghiaTranUIT]

Summary

• Add optional Homebrew Cask update flow for production releases
• Validate the configured Homebrew cask checkout before release work starts
• Update the cask version and SHA-256, then create a PR against Homebrew/homebrew-cask
• Document the new environment variable and non-interactive flags
• Add unit coverage for Homebrew cask parsing and update helpers

Testing

• Unit tests added for Homebrew cask content updates and branch naming
• Existing release helper tests updated to cover the new environment documentation

[briantkatch]

Would love to see this merged, would help a lot :)

[NghiaTranUIT]

@briantkatch I can merge it but I can't release on the cask yet, because it requires at least 100 stars on the public Github