Add an executable AI Failure Lab

[AdmilsonCossa]

Summary

• add bounded, editable AI failure scenarios with strict schema validation
• add an explicitly labelled deterministic browser policy preview
• add a one-click Node project that runs the same scenarios with published @workit/core@0.6.1
• add allowlisted Open-Meteo and GitHub Issues importers with payload, timeout, schema, and redaction boundaries
• enforce preview/runtime decision parity in tests and CI

Trust boundaries

• GitHub Pages presents a policy preview, not a WorkIt runtime execution
• real execution happens in the standalone Node project with an exact npm dependency and lockfile
• public-data imports accept no tokens and no arbitrary URLs
• evidence and payload sizes are bounded

Validation

• AI Failure Lab: 15/15 tests
• public-data adapters: 4/4 tests
• use-cases site: data contract, typecheck, and production build passed
• core: 410/410 tests passed
• full local verification passed all Node gates; the Bun compatibility fixture is environment-blocked on this new machine because Bun is not installed
• GitHub CI installs the pinned Bun and Deno runtimes and remains the multi-runtime authority

Scope

This PR does not change the @workit/core public API. It does not include private docs or editorial planning.