WIP: Add npm script + docs to run embedding integration test (bge-okh)

[SorraTheOrc]

Summary

• document the embedding integration test command and EMBED_NODE flag
• allow Node embedding integration tests on linux/arm64 by stubbing sharp during module load
• add beads for runtime embedding integration and demo server startup stabilization

Testing

• npm run test:integration:embedding
• npm test (unit passed; demo run hit EADDRINUSE but Playwright tests still ran and passed)

Notes

• Created follow-up beads: ge-hch.5.22 (Runtime: integrate embeddings into engine) and ge-hch.10 (Stabilize npm test demo server startup).
• test:demo hit EADDRINUSE on port 4173; follow-up bead tracks hardening.