Add multi-cluster observability with ringtail metrics and dashboards (#270)

## Summary
- Add `cluster` label (indri/ringtail) to all Prometheus scrape jobs, Alloy k8s metrics/logs, and Alloy host metrics/logs
- Deploy kube-state-metrics on ringtail's k3s cluster (ArgoCD app + manifests)
- Deploy Alloy on ringtail to collect pod metrics and logs, remote-writing to indri's Prometheus and Loki
- Replace single-cluster "Minikube Kubernetes" and "K8s Services Health" dashboards with:
  - **Kubernetes Clusters** dashboard — multi-cluster with `cluster` and `namespace` template variables
  - **Ringtail (k3s)** dashboard — dedicated ringtail view with GPU usage panels

## Deployment and Testing
1. Sync `apps` on indri ArgoCD to pick up new app definitions (`kube-state-metrics-ringtail`, `alloy-ringtail`)
2. Sync `prometheus` → verify `cluster` label on scraped metrics
3. Sync `alloy-k8s` → verify `cluster=indri` on remote-written metrics and logs
4. Run `mise run provision-indri -- --tags alloy` → verify `cluster=indri` on host Alloy metrics/logs
5. Sync `kube-state-metrics-ringtail` → verify pods running on ringtail
6. Sync `alloy-ringtail` → verify pods running, check Prometheus for `kube_pod_info{cluster="ringtail"}`
7. Sync `grafana-config` → verify dashboards appear, cluster variable populates both values
8. Check Loki for `{cluster="ringtail"}` logs from ringtail pods

## Notes
- Alloy on ringtail uses `insecure_skip_verify=true` for TLS to Prometheus/Loki (Tailscale-managed certs not in container trust store) — tighten later
- DNS resolution for `*.tail8d86e.ts.net` from ringtail pods depends on CoreDNS inheriting host's MagicDNS resolver; may need CoreDNS forwarding rules if pods can't resolve
- The old services dashboard (blackbox probes) is removed — those probes are still running in alloy-k8s and the data is still in Prometheus, just not in a dedicated dashboard

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/270

argocd/apps/alloy-ringtail.yaml

@@ -0,0 +1,17 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: alloy-ringtail
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: ssh://forgejo@forge.ops.eblu.me:2222/eblume/blumeops.git
+    targetRevision: main
+    path: argocd/manifests/alloy-ringtail
+  destination:
+    server: https://ringtail.tail8d86e.ts.net:6443
+    namespace: alloy
+  syncPolicy:
+    syncOptions:
+      - CreateNamespace=true

argocd/apps/kube-state-metrics-ringtail.yaml

@@ -0,0 +1,17 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: kube-state-metrics-ringtail
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: ssh://forgejo@forge.ops.eblu.me:2222/eblume/blumeops.git
+    targetRevision: main
+    path: argocd/manifests/kube-state-metrics-ringtail
+  destination:
+    server: https://ringtail.tail8d86e.ts.net:6443
+    namespace: monitoring
+  syncPolicy:
+    syncOptions:
+      - CreateNamespace=true