dotslash: publish Codex entrypoints from package archives

## Summary

DotSlash should resolve the same canonical package layout used by standalone installers and npm platform packages, but it should not take the size regression of downloading gzip-compressed package archives. Installers continue to use `.tar.gz` because that format is broadly available, while DotSlash can use zstd-compressed tar archives.

This updates the package archive release helper to emit both `*.tar.gz` and `*.tar.zst` package archives from the same package directory. The Codex CLI and `codex-app-server` DotSlash release config entries now match `codex-package-<target>.tar.zst` and `codex-app-server-package-<target>.tar.zst`, with paths that select `bin/codex` or `bin/codex-app-server` inside the extracted package. The Windows release compression loop also skips prebuilt `.tar.zst` archives so it does not try to recompress them as ordinary files.

The other helper outputs stay on their existing per-binary artifacts for now.

## Test plan

- `python3 -m json.tool .github/dotslash-config.json > /dev/null`
- `bash -n .github/scripts/build-codex-package-archive.sh`
- `python3 -m py_compile scripts/codex_package/cli.py`
- `ruby -e 'require "yaml"; YAML.load_file(".github/workflows/rust-release-windows.yml"); puts "ok"'`
- Ran a Python regex smoke test that checked every updated `codex` and `codex-app-server` platform entry against the `.tar.zst` archive names emitted by `.github/scripts/build-codex-package-archive.sh`.
- Ran `scripts/build_codex_package.py` with synthetic macOS entrypoint and `rg` binaries and repeated `--archive-output` values for `.tar.gz` and `.tar.zst`, verifying both archives were written.

.github/scripts/build-codex-package-archive.sh

@@ -97,9 +97,14 @@ else
   python_bin="python"
 fi
 
+if ! command -v zstd >/dev/null 2>&1 && [[ -x "${repo_root}/.github/workflows/zstd" ]]; then
+  export PATH="${repo_root}/.github/workflows:${PATH}"
+fi
+
 mkdir -p "$archive_dir"
 package_dir="${RUNNER_TEMP:-/tmp}/${archive_stem}-${target}"
-archive_path="${archive_dir}/${archive_stem}-${target}.tar.gz"
+gzip_archive_path="${archive_dir}/${archive_stem}-${target}.tar.gz"
+zstd_archive_path="${archive_dir}/${archive_stem}-${target}.tar.zst"
 rm -rf "$package_dir"
 
 "$python_bin" "${repo_root}/scripts/build_codex_package.py" \
@@ -108,5 +113,6 @@ rm -rf "$package_dir"
   --entrypoint-bin "${entrypoint_dir%/}/${entrypoint_name}${exe_suffix}" \
   --cargo-profile release \
   --package-dir "$package_dir" \
-  --archive-output "$archive_path" \
+  --archive-output "$gzip_archive_path" \
+  --archive-output "$zstd_archive_path" \
   --force