feat: Expose Grafana, Prometheus, and Flux UI via Tailscale LoadBalancer services

Replace Ansible port-forwarding + tailscale serve with direct Tailscale LB
services matching the existing Rancher pattern. Each service gets its own
tailnet hostname (grafana/prometheus/flux.silverside-gopher.ts.net).

infrastructure/addons/observability/grafana-tailscale-service.yaml

@@ -0,0 +1,18 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: grafana-tailscale
+  namespace: observability
+  annotations:
+    tailscale.com/hostname: grafana
+    tailscale.com/proxy-class: infra-stable
+spec:
+  type: LoadBalancer
+  loadBalancerClass: tailscale
+  selector:
+    app.kubernetes.io/name: grafana
+  ports:
+    - name: http
+      port: 80
+      protocol: TCP
+      targetPort: 3000