The server has no outbound internet access, so the curl download in
ensure_gum always failed silently and fell back to plain prompts.
Vendor the x86_64 release tarball under scripts/vendor/ and check it
before attempting a download - download stays as a fallback for other
archs or a version bump without a re-vendor.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bs8xf8Dt8X6tRBvBiLCXYc
