test: verify declared package entrypoints are packed

[rogerchappel]

Summary

• Add deterministic npm pack --dry-run --json verification that every declared bin and exports file is present in package contents.
• Run the assertion as the existing package smoke/release verification step.

Verification

• npm run release:check — passed (23 tests, build, smoke, package-content assertion).
• git diff --check — passed.
• Reviewed workflow trigger: CI only; no release/deploy/publish workflow is triggered by branch push or draft PR.

Commits:

• test: verify declared package entrypoints are packed — add package manifest-content assertion and wire into package smoke.

Files changed: package.json, scripts/check-package-content.js.

Risk Level

• Low

Rollback Plan

• Revert the commit; existing npm pack dry-run behavior can be restored.

Human Decision Needed

• Maintainer review