feat: add standalone UDP multicast competency test script

[alibaba0010]

This PR replaces the previous task3.js implementation with a standalone Node.js UDP multicast competency test script.

The new script:

• uses Node’s dgram module
• binds to a multicast group and port
• broadcasts a dummy Nostr event as JSON over UDP
• receives its own multicast payload (loopback enabled)
• parses and validates the received JSON event shape
• exits cleanly with success/failure status codes and helpful logs

Defaults are configurable via environment variables:

• MULTICAST_GROUP (default: 239.255.0.1)
• MULTICAST_PORT (default: 29999)
• RECEIVE_TIMEOUT_MS (default: 5000)

Related Issue

N/A (competency test submission task)

Motivation and Context

The competency test requires a standalone script that demonstrates multicast UDP broadcast + self-receive + JSON parsing for a dummy Nostr event.
This change provides that exact behavior in a single runnable script while following repository style and validation expectations.

How Has This Been Tested?

Validated locally using project/CI-aligned checks:

• npm run lint
• npm run build:check
• npm run test:unit
• npm run knip (run from a clean temp worktree due local .nostr/data permission constraints)
• npm run docker:test:integration (69 scenarios passed)
• npm run docker:cover:integration
• npm run cover:unit (run from clean temp worktree for same local permission constraint)
• node task3.js (confirmed multicast send, self-receive, JSON parse, and success exit)

Screenshots (if appropriate):

N/A

Types of changes

• New feature (non-breaking change which adds functionality)
• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 16e0552

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