grafana: deploy Grafana instance, datasource and dashboards (#238)

## Why
Deploys Grafana in-cluster (observability project) via the grafana-operator, mirroring the puppet Grafana but modernised — **CNPG** for state, **Authentik OIDC** for auth — and ports the live datasource + dashboards in as CRs.

Depends on: grafana-operator (#235, merged), grafana schemas (#236, merged), Authentik OIDC (terraform-authentik #2), Vault seeds (done), and `^grafana/` image proxy (terraform-artifactapi #5).

## Changes (`apps/base/grafana`)
- **CNPG** postgres Cluster + rw Pooler (db `grafana`); **VaultAuth** + **VaultStaticSecrets** pulling `postgres`/`oauth` credentials from `kv/kubernetes/namespace/grafana/default/*`.
- **Grafana CR**: postgres backend via the pooler; Authentik `generic_oauth` (client id/secret from the Vault-synced secret, openid/email/profile scopes, group→role mapping); `root_url` grafana.k8s.syd1.au.unkin.net.
- **1 GrafanaDatasource** — k8s VictoriaMetrics via the operator `vmselect-main` service; reuses the previous default datasource uid so the imported dashboards resolve unedited.
- **13 GrafanaDashboards** (gzipJson) exported from the current grafana.
- **Gateway API** (traefik-internal) + HTTPRoute for grafana.k8s.syd1.au.unkin.net.
- Registered in the observability ApplicationSet + project.

## Review notes
- OAuth `role_attribute_path` maps Authentik group `grafana-admins` → Admin, else Viewer — **confirm the group name**.
- `database.ssl_mode: require` against the CNPG pooler — adjust if the pooler isn't serving TLS.
- The `VictoriaLogs - cluster` dashboard has no in-cluster logs datasource yet (no VictoriaLogs in k8s) — included for completeness, will be empty until one exists.
- `make kubeconform` clean (24 resources, validated against the strict grafana schemas).

Reviewed-on: #238
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

apps/base/grafana/cnpg_cluster.yaml

@@ -0,0 +1,58 @@
+---
+apiVersion: postgresql.cnpg.io/v1
+kind: Cluster
+metadata:
+  name: postgres
+  namespace: grafana
+spec:
+  affinity:
+    podAntiAffinityType: preferred
+  bootstrap:
+    initdb:
+      database: grafana
+      encoding: UTF8
+      localeCType: C
+      localeCollate: C
+      owner: grafana
+      secret:
+        name: postgres-credentials
+  enablePDB: true
+  enableSuperuserAccess: false
+  failoverDelay: 0
+  imageName: ghcr.io/cloudnative-pg/postgresql:18.1-system-trixie
+  instances: 2
+  logLevel: info
+  monitoring:
+    customQueriesConfigMap:
+      - key: queries
+        name: cnpg-default-monitoring
+    disableDefaultQueries: false
+    enablePodMonitor: false
+  postgresql:
+    parameters:
+      max_connections: "200"
+      shared_buffers: 128MB
+  primaryUpdateMethod: restart
+  primaryUpdateStrategy: unsupervised
+  replicationSlots:
+    highAvailability:
+      enabled: true
+      slotPrefix: _cnpg_
+    synchronizeReplicas:
+      enabled: true
+    updateInterval: 30
+  resources:
+    limits:
+      cpu: 500m
+      memory: 512Mi
+    requests:
+      cpu: 100m
+      memory: 256Mi
+  smartShutdownTimeout: 180
+  startDelay: 3600
+  stopDelay: 1800
+  storage:
+    resizeInUseVolumes: true
+    size: 10Gi
+    storageClass: cephrbd-fast-delete
+  switchoverDelay: 3600