feat: add executable smoke test module

[flyzorro]

Summary

• add the source-level src/smoke-test.js ESM entrypoint with a run() export
• add focused smoke test coverage and wire npm test to run it
• record the implementation details in the story progress log

Why

This gives the repo a stable smoke-test module that can be imported directly and confirms the required command prints the expected success message.

Testing

• npm run build
• npm test
• node -e "import('/Users/zky/antfarm/src/smoke-test.js').then(m => m.run())"

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