refactor: Replace CNPG external DB with rancher-backup operator

Rancher 2.x uses embedded etcd, not an external PostgreSQL database.
The CATTLE_DB_CATTLE_* env vars are Rancher v1 only and were ignored.

- Remove all CNPG (CloudNativePG) cluster, operator, and related configs
- Remove external DB env vars from Rancher HelmRelease
- Remove rancher-db-password ExternalSecret
- Add rancher-backup operator HelmRelease (v106.0.2+up8.1.0)
- Add B2 credentials ExternalSecret for backup storage
- Add recurring Backup CR (daily at 03:00, 7 day retention)
- Add commented-out Restore CR for rebuild recovery
- Update Flux dependency graph accordingly

infrastructure/addons/rancher/helmrelease-rancher.yaml

@@ -26,19 +26,6 @@ spec:
     tls: external
     replicas: 1
     extraEnv:
-      - name: CATTLE_DB_CATTLE_HOST
-        value: cnpg-cluster-rw.cnpg-cluster.svc
-      - name: CATTLE_DB_CATTLE_PORT
-        value: "5432"
-      - name: CATTLE_DB_CATTLE_DATABASE
-        value: postgres
-      - name: CATTLE_DB_CATTLE_USERNAME
-        value: postgres
-      - name: CATTLE_DB_CATTLE_PASSWORD
-        valueFrom:
-          secretKeyRef:
-            name: rancher-db-password
-            key: password
       - name: CATTLE_PROMETHEUS_METRICS
         value: "true"
     resources:

infrastructure/addons/rancher/kustomization.yaml

@@ -6,5 +6,4 @@ resources:
   - helmrelease-rancher.yaml
   - rancher-bootstrap-password-flux-externalsecret.yaml
   - rancher-bootstrap-password-externalsecret.yaml
-  - rancher-db-password-externalsecret.yaml
   - rancher-tailscale-service.yaml

infrastructure/addons/rancher/rancher-db-password-externalsecret.yaml

@@ -1,21 +0,0 @@
-apiVersion: external-secrets.io/v1
-kind: ExternalSecret
-metadata:
-  name: rancher-db-password
-  namespace: cattle-system
-spec:
-  refreshInterval: 1h
-  secretStoreRef:
-    name: doppler-hetznerterra
-    kind: ClusterSecretStore
-  target:
-    name: rancher-db-password
-    creationPolicy: Owner
-    template:
-      type: Opaque
-      data:
-        password: "{{ .RANCHER_DB_PASSWORD }}"
-  data:
-    - secretKey: RANCHER_DB_PASSWORD
-      remoteRef:
-        key: RANCHER_DB_PASSWORD