Bundle-export freshness gate

Bundle-export regressions must inspect artifacts built from the current checkout. Freshness must cover every asserted generated artifact—including dist/embedding-worker.cjs and dist/embedding-worker.js—not only index bundles; otherwise fresh indexes can suppress rebuilding while stale workers pass tests. Compare against relevant repository sources, scripts, and manifests, but intentionally exclude node_modules mtimes because dependency installation does not define checkout-source freshness.