fix(release): restore single-package npm build with vendor binaries
Upstream 0.99 refactored build_npm_package.py to split native binaries
into per-platform sub-packages (codex-linux-x64, codex-win32-arm64, etc.)
and made the main "codex" package only contain JS wrappers (files: ["bin"]).
Our fork publishes a single @cometix/codex package that must bundle all
platform binaries in vendor/. Revert build_npm_package.py to the 0.98
version which copies native binaries directly into the package.
Also remove unused NPM_PACKAGE_NAME and GITHUB_REPO constants from
updates.rs (dead code left over from the merge).