feat(helm): fix ServiceMonitor selector and add observability config (P7.4, miroir-afh.4)

- Add `app.kubernetes.io/component: metrics` label to miroir-service.yaml for
  ServiceMonitor discovery (plan §10)
- Update ServiceMonitor selector to match `component: metrics` instead of
  `component: miroir` (plan §10 specification)
- Add `serviceMonitor.enabled: false` config flag to values.yaml
- Add `prometheusRule.enabled: false` config flag to values.yaml
- Add JSON schema entries for serviceMonitor and prometheusRule to
  values.schema.json

All 12 alerts are present in miroir-prometheusrule.yaml:
  Availability (7): DegradedShards, NodeDown, HighSearchLatency,
    TaskStuck, RebalanceStuck, SettingsDivergence, AntientropyMismatch
  Resource pressure (5): MemoryPressure, RequestQueueBacklog,
    BackgroundJobBacklog, PeerDiscoveryGap, NoLeader

Acceptance:
  ✓ ServiceMonitor selector matches plan §10 (component: metrics)
  ✓ All 12 alerts present in PrometheusRule
  ✓ Schema validation tests pass (9 passed)
  ✓ Helm flags default to false (opt-in for prometheus-operator)

Phase 9 chaos tests will verify each alert trips as expected (separate bead).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

charts/miroir/templates/miroir-service.yaml

@@ -9,6 +9,7 @@ metadata:
   labels:
     {{- include "miroir.labels" . | nindent 4 }}
     app.kubernetes.io/component: miroir
+    app.kubernetes.io/component: metrics
   {{- with .Values.service.annotations }}
   annotations:
     {{- toYaml . | nindent 4 }}

charts/miroir/templates/miroir-servicemonitor.yaml

@@ -1,5 +1,6 @@
 {{/*
 Miroir ServiceMonitor (requires prometheus-operator)
+Plan §10: metrics scraping via ServiceMonitor
 */}}
 {{- if .Values.serviceMonitor.enabled }}
 apiVersion: monitoring.coreos.com/v1
@@ -17,7 +18,7 @@ spec:
   selector:
     matchLabels:
       {{- include "miroir.selectorLabels" . | nindent 6 }}
-      app.kubernetes.io/component: miroir
+      app.kubernetes.io/component: metrics
   endpoints:
     - port: metrics
       interval: {{ .Values.serviceMonitor.interval | default "30s" }}

charts/miroir/values.schema.json

@@ -362,6 +362,21 @@
         "annotations": {"type": "object"},
         "name": {"type": "string"}
       }
+    },
+    "serviceMonitor": {
+      "type": "object",
+      "properties": {
+        "enabled": {"type": "boolean"},
+        "interval": {"type": "string"},
+        "annotations": {"type": "object"}
+      }
+    },
+    "prometheusRule": {
+      "type": "object",
+      "properties": {
+        "enabled": {"type": "boolean"},
+        "annotations": {"type": "object"}
+      }
     }
   }
 }

charts/miroir/values.yaml

@@ -187,3 +187,14 @@ serviceAccount:
   create: true
   annotations: {}
   name: ""
+
+# ServiceMonitor (plan §10)
+serviceMonitor:
+  enabled: false  # requires prometheus-operator in cluster
+  interval: 30s
+  annotations: {}
+
+# PrometheusRule (plan §10 + §14.9)
+prometheusRule:
+  enabled: false  # requires prometheus-operator in cluster
+  annotations: {}