ci: skip npm publish when token is missing

[papperrollinggery]

Summary

• Prevent Release workflow failures when prerelease tags are pushed before NPM_TOKEN is configured.
• Publish step now emits a notice and exits 0 if NODE_AUTH_TOKEN is empty.

Cause

• v2.0.0-beta.1 tag triggered Release.
• Release attempted npm publish with empty NODE_AUTH_TOKEN.
• npm failed with ENEEDAUTH.

Verification

• npm run audit:public
• git diff --check
• commit hook: npm run build, npm test, npm run lint