Add dashboards and alerts as code, mark Phase 6 done

Dashboards: observability/dashboards/generate.py (Grafana Foundation SDK)
writes k8s/grafana/dashboards/*.json -- a RED dashboard per HTTP service
and a system overview -- shipped through a file provider and
configMapGenerators, so `kubectl apply -k k8s/` rebuilds them. Verified by
deleting Grafana and its volume and re-applying. Adds tracesToMetrics to
the Tempo datasource.

Alerts: Prometheus rule files delivering to Alertmanager, under a
labels/annotations contract enforced by observability/alerts/check_contract.py,
with runbooks in docs/runbooks/.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

k8s/grafana/deployment.yaml

@@ -51,6 +51,10 @@ spec:
               mountPath: /var/lib/grafana
             - name: datasources
               mountPath: /etc/grafana/provisioning/datasources
+            - name: dashboards-provider
+              mountPath: /etc/grafana/provisioning/dashboards
+            - name: dashboards
+              mountPath: /etc/grafana/dashboards/
       volumes:
         - name: data
           persistentVolumeClaim:
@@ -58,3 +62,9 @@ spec:
         - name: datasources
           configMap:
             name: grafana-datasources
+        - name: dashboards-provider
+          configMap:
+            name: grafana-dashboards-provider
+        - name: dashboards
+          configMap:
+            name: grafana-dashboards