feat: split Grafana dashboards into per-folder ConfigMaps

Replace monolithic dashboards-configmap.yaml with 10 dedicated files,
one per Grafana folder: Ingress, Observability, Infrastructure, Storage,
Identity, DevTools, Search, Media, La Suite, Communications.

New dashboards for Longhorn, PostgreSQL/CNPG, Cert-Manager, SeaweedFS,
Hydra, Kratos, Gitea, OpenSearch, LiveKit, La Suite golden signals
(Linkerd metrics), Matrix, and Email Pipeline.

base/monitoring/kustomization.yaml

@@ -7,7 +7,22 @@ resources:
   - namespace.yaml
   - vault-secrets.yaml
   - grafana-oauth2client.yaml
-  - dashboards-configmap.yaml
+  # Dashboards (one ConfigMap per Grafana folder)
+  - dashboards-ingress.yaml
+  - dashboards-observability.yaml
+  - dashboards-infrastructure.yaml
+  - dashboards-storage.yaml
+  - dashboards-identity.yaml
+  - dashboards-devtools.yaml
+  - dashboards-search.yaml
+  - dashboards-media.yaml
+  - dashboards-lasuite.yaml
+  - dashboards-comms.yaml
+  # AlertManager → Matrix bridge
+  - matrix-alertmanager-receiver-deployment.yaml
+  - matrix-bot-secret.yaml
+  # Alert rules
+  - alertrules-infrastructure.yaml
 
 helmCharts:
   # helm repo add prometheus-community https://prometheus-community.github.io/helm-charts