(orchestration): Tiered human review routing by PR risk

## Component

API or orchestration

## Describe the feature

Route PRs to **different human review requirements** based on **PR risk classification** (and optional code-area rules): auto-notify only senior reviewers for critical paths, skip human for docs-only low-risk, etc.

## Use case

Review is the new bottleneck. Teams experiment with **risk compartments** in the codebase—more scrutiny on critical paths, lighter review on internal/docs changes—and conserving human attention.

## Proposed solution

1. Extend **PR risk classification** (roadmap) output to `review_tier: minimal | standard | elevated`.
2. Blueprint maps tiers to: required reviewers (GitHub teams), Cedar approval rules, notification templates.
3. Optional: auto-merge when tier=minimal and all automated gates pass (Cedar-gated).

## Other information

- Builds on roadmap **PR risk classification**; this draft adds **routing** UX not spelled out in ROADMAP.md.
- Pairs with **feature-pre-human-automated-review-gate**.

## Acknowledgements

- [ ] I may be able to implement this feature
- [ ] This might be a breaking change

## Acceptance criteria

- [ ] Risk tier persisted on task/PR metadata.
- [ ] Notification plane respects tier (who gets heads-up).
- [ ] Documented examples for docs-only vs. auth-critical paths.
- [ ] Tests for classifier → routing mapping.

Empieza leyendo ROADMAP.md para conocer el trabajo de clasificación de riesgos de los PR y revisa la funcionalidad enlazada de la puerta de revisión automatizada previa a la revisión humana. Rastrea dónde se representan los metadatos de riesgo, las notificaciones y las reglas de aprobación de Cedar, y usa después los criterios de aceptación como la definición de terminado: niveles persistidos, notificaciones adaptadas al nivel, ejemplos documentados y pruebas desde el clasificador hasta el enrutamiento.

Escrito por el modelo de indexación a partir del texto del issue.