feat(minecraft): add Prometheus metrics + Grafana dashboard

- minecraft-prometheus-exporter v3.1.2 plugin (port 9225)
- ServiceMonitor for Prometheus scraping
- Grafana dashboard ConfigMap (ID 20659, Minecraft server stats)
- metrics port added to Service and Deployment containerPorts

cluster/applications/minecraft/servicemonitor.yaml

@@ -0,0 +1,23 @@
+---
+# ServiceMonitor — tells Prometheus to scrape minecraft-prometheus-exporter
+# Plugin exposes /metrics on port 9225 (HTTP)
+# Dashboard: https://grafana.com/grafana/dashboards/20659
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: minecraft
+  namespace: minecraft
+  labels:
+    app.kubernetes.io/name: minecraft
+    app.kubernetes.io/component: papermc
+    # Label required for kube-prometheus-stack to discover this ServiceMonitor
+    release: monitoring
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: minecraft
+      app.kubernetes.io/component: papermc
+  endpoints:
+    - port: metrics
+      path: /metrics
+      interval: 15s