`yarn artifacts` (napi-cli v3 `napi artifacts`) writes each per-target
.node file into `npm/<triple>/`. The repo has hand-written templates
for most triples but darwin-universal was added to `napi.targets`
without one, so the publish step failed with:

  ENOENT: no such file or directory, open
  '.../bindings/node/npm/darwin-universal/tokenizers.darwin-universal.node'

Add `napi create-npm-dirs` before `yarn artifacts` — it scans
`napi.targets` and creates any missing dirs (with a generated
package.json) from scratch. Idempotent for triples that already have
hand-written templates.