Add compensating controls framework and date-based report dirs (#320)

## Summary

- Add `compensating-controls.yaml` tracking 9 named controls that justify suppressed security findings
- Update all Prowler mutelist descriptions with `CC: <id>` references to named controls
- Add `mise run review-compensating-controls` task — surfaces stalest control with all codebase references
- Add [[review-compensating-controls]] how-to doc
- Organize Prowler and Kingfisher reports into `YYYY-MM-DD` subdirectories

### Compensating controls

| ID | Mitigates |
|----|-----------|
| `single-user-cluster` | Image cache abuse, RBAC breadth, system pod privileges |
| `tailscale-network-isolation` | Profiling endpoints, weak TLS, debug ports |
| `local-registry` | AlwaysPullImages gap |
| `sso-gated-admin-tools` | ArgoCD wildcard RBAC |
| `operator-managed-pods` | Tailscale proxy pod security settings |
| `ephemeral-privileged-jobs` | Prowler hostPID exposure |
| `trusted-ci-only` | Forgejo runner DinD |
| `init-container-isolation` | Grafana root init container |
| `observability-stack-audit` | Missing apiserver audit logging |

## Test plan

- [ ] `mise run review-compensating-controls` shows table and references
- [ ] `kubectl kustomize argocd/manifests/prowler/` renders correctly
- [ ] Sync prowler and kingfisher, verify next scan writes to dated subdirectory
- [ ] Grep for `CC:` in mutelist files — every muted finding should have at least one

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #320

docs/reference/operations/security.md

@@ -46,6 +46,14 @@ Security posture and compliance scanning for BlumeOps infrastructure.
 
 All compliance scan reports are stored on `sifaka:/volume1/reports/`. See [[read-compliance-reports]] for access and interpretation.
 
+## Compensating controls
+
+Suppressed findings reference named compensating controls tracked in `compensating-controls.yaml` (repo root). Each control has a review date and verification steps. See [[review-compensating-controls]] for the review process.
+
+```bash
+mise run review-compensating-controls
+```
+
 ## Known gaps
 
 - No SOC 2 compliance mapping for Kubernetes (Prowler only maps SOC 2 for AWS/Azure/GCP)