Add package smoke test for npm pack contents and CLI startup

[dejaguarkyng]

The package build is tested, but the published artifact shape and CLI startup path should have a smoke test. Add a check that verifies npm pack contents and the bin entrypoint behavior before publish.

Acceptance criteria:

• Add a test or CI step that runs npm pack --dry-run or equivalent and verifies expected dist files are included while test files are excluded.
• Add a CLI startup smoke check that confirms missing JUNGLE_GRID_API_KEY exits with the documented error.
• Keep the check fast enough for CI.
• Document the verification command in the publishing section if needed.