fix: monitoring — Ingress Prometheus/AlertManager, paths + pathType requis

Le chart kube-prometheus-stack nécessite paths:[/] et pathType:Prefix
contrairement au sous-chart Grafana qui a des defaults.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

k8s/infra/monitoring/values.yaml

@@ -25,6 +25,9 @@ prometheus:
     ingressClassName: traefik
     hosts:
       - prometheus.lab.local
+    paths:
+      - /
+    pathType: Prefix
 
   prometheusSpec:
     retention: 15d
@@ -97,6 +100,9 @@ alertmanager:
     ingressClassName: traefik
     hosts:
       - alertmanager.lab.local
+    paths:
+      - /
+    pathType: Prefix
 
   alertmanagerSpec:
     resources: