feat: add den control plane with real Render-backed workers

[benjaminshafii]

Summary

• Add a Den control-plane service with Better Auth + Drizzle-backed worker APIs and a hosted demo page for signup/auth/create-worker flow.
• Replace stub provisioning with a real Render provisioner that creates services, polls deploy status, and verifies worker /health before marking cloud workers healthy.
• Add non-stub end-to-end evidence artifacts (API/CLI report + web screenshots) showing authenticated worker creation returns provider: render and healthy worker instances.

Testing & evidence

• Captured machine-readable E2E output in evidence/den-e2e-nonstub/report.json.
• Captured web flow screenshots in evidence/den-e2e-nonstub/webapp/.
• Captured worker health payload in evidence/den-e2e-nonstub/07-web-worker-health.json.

[benjaminshafii]

Closing as superseded: implementation moved to different-ai/openwork in different-ai/openwork#632 per repo-target correction.