k8s/monitoring: add prometheus grafana loki observability

- Loki log aggregation (MinIO backed, 10-day retention)
- Promtail daemonset (pod + talos journal logs)
- Prometheus + kube-state-metrics
- Grafana dashboards (6-row template per service)

k8s/monitoring/alerts/svc-forgejo-rules.yaml

@@ -0,0 +1,23 @@
+apiVersion: monitoring.coreos.com/v1
+kind: PrometheusRule
+metadata:
+  name: forgejo-rules
+  namespace: forgejo
+spec:
+  groups:
+    - name: forgejo.rules
+      interval: 15s
+      rules:
+        - alert: ForgejoHighErrorRate
+          expr: |
+            (
+              sum(rate(forgejo_http_request_total{status=~"5.."}[5m]))
+              /
+              sum(rate(forgejo_http_request_total[5m]))
+            ) > 0.05
+          for: 10m
+          labels:
+            severity: warning
+          annotations:
+            summary: "High error rate on Forgejo"
+            description: "5xx error rate exceeded 5% for 10 minutes. Value: {{ $value | humanizePercentage }}"