docs(08): create phase plan

Phase 08: Observability Stack
- 3 plans in 2 waves
- Wave 1: 08-01 (metrics), 08-02 (Alloy) - parallel
- Wave 2: 08-03 (verification) - depends on both
- Ready for execution

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -89,12 +89,12 @@ Plans:
   3. Logs from all pods are queryable in Grafana Explore via Loki
   4. Alert fires when a pod crashes or restarts repeatedly (KubePodCrashLooping)
   5. TaskPlanner /metrics endpoint returns Prometheus-format metrics
-**Plans**: TBD
+**Plans**: 3 plans
 
 Plans:
-- [ ] 08-01: kube-prometheus-stack installation (Prometheus + Grafana)
-- [ ] 08-02: Loki + Alloy installation for log aggregation
-- [ ] 08-03: Critical alerts and TaskPlanner metrics endpoint
+- [ ] 08-01-PLAN.md — TaskPlanner /metrics endpoint and ServiceMonitor
+- [ ] 08-02-PLAN.md — Promtail to Alloy migration for log collection
+- [ ] 08-03-PLAN.md — End-to-end observability verification
 
 ### Phase 9: CI Pipeline Hardening
 **Goal**: Tests run before build - type errors and test failures block deployment
@@ -126,13 +126,14 @@ Phases execute in numeric order: 7 -> 8 -> 9
 | 5. Search | v1.0 | 3/3 | Complete | 2026-01-31 |
 | 6. Deployment | v1.0 | 2/2 | Complete | 2026-02-01 |
 | 7. GitOps Foundation | v2.0 | 2/2 | Complete ✓ | 2026-02-03 |
-| 8. Observability Stack | v2.0 | 0/3 | Not started | - |
+| 8. Observability Stack | v2.0 | 0/3 | Planned | - |
 | 9. CI Pipeline Hardening | v2.0 | 0/2 | Not started | - |
 
 ---
 *Roadmap created: 2026-01-29*
 *v2.0 phases added: 2026-02-03*
 *Phase 7 planned: 2026-02-03*
+*Phase 8 planned: 2026-02-03*
 *Depth: standard*
 *v1.0 Coverage: 31/31 requirements mapped*
 *v2.0 Coverage: 17/17 requirements mapped*