Add sample action package: `vu1nz-scan`

[ralyodio]

Create an MVP sample action package called vu1nz-scan based on the manifest and structure outlined in the PRD. This should include:

• A directory at packages/actions/vu1nz-scan/
• Manifest (sh1pt.action.json)
• Workflow YAML (workflows/vu1nz-scan.yml)
• README file
• Registry entry in packages/registry/actions.json

Reference: #422