add nightly Vault raft snapshot backup to R2

Snapshot via vault operator raft snapshot save using a least-privilege
periodic token. Stored in legion-vault-backup R2 bucket via restic.
Retains 30 daily / 12 weekly / 6 monthly snapshots. Runs at 3am,
offset from the Gitea backup at 2am.

servers/legion/k8s/vault/backup-cronjob.yaml

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+---
+# Nightly Vault backup — raft snapshot → Cloudflare R2 via restic
+# Schedule: 3am daily (offset from Gitea backup at 2am).
+# Retains 30 daily / 12 weekly / 6 monthly snapshots.
+apiVersion: batch/v1
+kind: CronJob
+metadata:
+  name: vault-backup
+  namespace: vault
+spec:
+  schedule: "0 3 * * *"
+  concurrencyPolicy: Forbid
+  failedJobsHistoryLimit: 3
+  successfulJobsHistoryLimit: 3
+  jobTemplate:
+    spec:
+      backoffLimit: 2
+      template:
+        spec:
+          restartPolicy: OnFailure
+          serviceAccountName: default
+          initContainers:
+            - name: vault-snapshot
+              image: hashicorp/vault:latest
+              command:
+                - /bin/sh
+                - -c
+                - |
+                  set -e
+                  echo "Taking Vault raft snapshot..."
+                  VAULT_TOKEN=$VAULT_SNAPSHOT_TOKEN \
+                  vault operator raft snapshot save /snapshot/vault.snap
+                  echo "Snapshot complete, size: $(du -sh /snapshot/vault.snap)"
+              env:
+                - name: VAULT_ADDR
+                  value: "http://vault.vault.svc.cluster.local:8200"
+                - name: VAULT_SNAPSHOT_TOKEN
+                  valueFrom:
+                    secretKeyRef:
+                      name: vault-backup-credentials
+                      key: VAULT_SNAPSHOT_TOKEN
+              volumeMounts:
+                - name: snapshot
+                  mountPath: /snapshot
+              resources:
+                requests:
+                  memory: 64Mi
+                  cpu: 50m
+                limits:
+                  memory: 256Mi
+          containers:
+            - name: backup
+              image: restic/restic:latest
+              command:
+                - /bin/sh
+                - -c
+                - |
+                  set -e
+
+                  # Init repo if first run
+                  restic snapshots 2>/dev/null || restic init
+
+                  echo "Running restic backup..."
+                  restic backup \
+                    /snapshot/vault.snap \
+                    --tag vault \
+                    --tag legion \
+                    --host legion
+
+                  # Prune old snapshots
+                  restic forget \
+                    --keep-daily 30 \
+                    --keep-weekly 12 \
+                    --keep-monthly 6 \
+                    --prune
+
+                  echo "Backup complete."
+                  restic snapshots --latest 3
+              envFrom:
+                - secretRef:
+                    name: vault-backup-credentials
+              volumeMounts:
+                - name: snapshot
+                  mountPath: /snapshot
+                  readOnly: true
+              resources:
+                requests:
+                  memory: 128Mi
+                  cpu: 100m
+                limits:
+                  memory: 256Mi
+          volumes:
+            - name: snapshot
+              emptyDir: {}

servers/legion/k8s/vault/backup-external-secrets.yaml

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+---
+# vault-backup-credentials — R2 keys + restic password + Vault snapshot token
+apiVersion: external-secrets.io/v1beta1
+kind: ExternalSecret
+metadata:
+  name: vault-backup-credentials
+  namespace: vault
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    name: vault
+    kind: ClusterSecretStore
+  target:
+    name: vault-backup-credentials
+    creationPolicy: Owner
+    template:
+      data:
+        VAULT_SNAPSHOT_TOKEN: "{{ .snapshot_token }}"
+        RESTIC_PASSWORD: "vault-restic-2026"
+        AWS_ACCESS_KEY_ID: "{{ .r2_access_key_id }}"
+        AWS_SECRET_ACCESS_KEY: "{{ .r2_secret_access_key }}"
+        RESTIC_REPOSITORY: "s3:https://651161e0a3d321561b4c90b5bcd5f15b.r2.cloudflarestorage.com/legion-vault-backup"
+  data:
+    - secretKey: snapshot_token
+      remoteRef:
+        key: secret/data/vault/snapshot-token
+        property: token
+    - secretKey: r2_access_key_id
+      remoteRef:
+        key: secret/data/r2
+        property: access_key_id
+    - secretKey: r2_secret_access_key
+      remoteRef:
+        key: secret/data/r2
+        property: secret_access_key