fix: write npmrc config with VP_TOKEN env var placeholder

- Write @voidzero-dev:registry and auth token config to ~/.npmrc
- Use ${VP_TOKEN} placeholder in .npmrc for the auth token
- Pass actual token via VP_TOKEN environment variable during npm install
- This approach keeps the config persistent while protecting the token

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: fengmk2