Add observability stack: ServiceMonitors, Tempo, OTel API instrumentation, dashboards

- Add ServiceMonitors for Traefik, ArgoCD, and Longhorn
- Enable cert-manager ServiceMonitor via helm values
- Deploy Grafana Tempo for distributed tracing (single-binary, Longhorn PVC)
- Add Tempo datasource with trace-to-logs and trace-to-metrics correlation
- Instrument API with OpenTelemetry SDK (Prometheus metrics + OTLP traces)
- Replace console.log with pino structured logging + pino-http middleware
- Add Grafana dashboards for Traefik, API overview, and PostgreSQL (CNPG)

infra/kubernetes/observability/tempo/application.yaml

@@ -0,0 +1,41 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: tempo
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: https://grafana.github.io/helm-charts
+    chart: tempo
+    targetRevision: 1.12.0
+    helm:
+      valuesObject:
+        tempo:
+          receivers:
+            otlp:
+              protocols:
+                grpc:
+                  endpoint: "0.0.0.0:4317"
+                http:
+                  endpoint: "0.0.0.0:4318"
+          retention: 168h
+          resources:
+            requests:
+              memory: 256Mi
+              cpu: 100m
+            limits:
+              memory: 1Gi
+        persistence:
+          enabled: true
+          storageClassName: longhorn
+          size: 10Gi
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: observability
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=true