media: add nightly config backup to Cloudflare R2 via restic

Backs up all service config PVCs (Jellyfin, Radarr, Sonarr, Prowlarr,
qBittorrent, Bazarr, Seerr) at 3am daily to legion-media-backup R2 bucket.
Media files are excluded — they are re-downloadable.

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

@@ -0,0 +1,29 @@
+# media-backup-credentials — R2 + restic credentials for nightly media config backup
+apiVersion: external-secrets.io/v1beta1
+kind: ExternalSecret
+metadata:
+  name: media-backup-credentials
+  namespace: media
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    name: vault
+    kind: ClusterSecretStore
+  target:
+    name: media-backup-credentials
+    creationPolicy: Owner
+    template:
+      data:
+        RESTIC_PASSWORD: "media-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-media-backup"
+  data:
+    - 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