[Security] Harden downloadFile and downloadGitHubRelease

[gonzaloriestra]

This PR hardens the file download logic in the CLI.

1. downloadFile status validation: Added a check for res.ok in the downloadFile utility. Previously, it would proceed to pipe the response body even if the request failed (e.g., 404 or 500), potentially saving an HTML error page to the target path.
2. Streaming GitHub Release downloads: Refactored downloadGitHubRelease to use the downloadFile utility. This switches the download mechanism from response.arrayBuffer() to a streaming pipeline, which is more memory-efficient and prevents potential Denial of Service (DoS) when downloading large assets.

Tests have been updated to verify these changes.

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PR created automatically by Jules for task 16758916623768002703 started by @gonzaloriestra

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