docs: Reconcile backups and backup-and-restore pages

backups.md kept its store-level table and danger note but now points to
vantagectl as the supported path, with mongodump/mongorestore demoted to
an explicit fallback and a warning that a plain dump records no key
fingerprint. backup-and-restore.md links back for the store-level
overview.

docsite/docs/operations/backup-and-restore.md

@@ -9,6 +9,9 @@ MongoDB database behind a Vantage control plane. It talks to MongoDB directly,
 never to the Vantage API, so it works against a control plane that is down,
 half-migrated, or gone — exactly the situation a backup tool has to survive.
 
+For the store-level overview — what holds what, and why the database alone is
+not a backup — see [Backups](./backups.md). This page covers the tool.
+
 :::danger The key comes first
 Vantage encrypts SSH private keys, key passphrases, vault secrets, SSO client
 secrets and console credentials with `KEY_ENCRYPTION_KEY`. **It is not in your

docsite/docs/operations/backups.md

@@ -24,7 +24,23 @@ values is permanently unreadable.
 Store the key somewhere other than the server it protects.
 :::
 
-## Backing up MongoDB
+:::info Use `vantagectl`
+[**Backup and restore**](./backup-and-restore.md) is the supported way to take
+and restore a backup. It writes an archive that carries a fingerprint of
+`KEY_ENCRYPTION_KEY` — never the key — so a restore taken with the wrong key
+**refuses** rather than silently producing a database whose secrets nobody can
+read. It also checksums every archive member before writing anything, and
+refuses to restore into a database that already holds data. A plain
+`mongodump` does none of that: it records nothing about which key the data was
+encrypted under, so a restore from one succeeds even when the key is wrong and
+the failure only shows up later, as unreadable secrets.
+
+The rest of this page, past the table above, describes the `mongodump` /
+`mongorestore` fallback for an operator who does not have `vantagectl`
+available. Prefer the linked page.
+:::
+
+## Backing up MongoDB (fallback, without `vantagectl`)
 
 With the bundled Mongo container:
 
@@ -33,6 +49,13 @@ docker compose exec -T mongo mongodump --archive --gzip --db vantage \
   > /backups/vantage-$(date +%F).archive.gz
 ```
 
+:::warning
+This archive records nothing about which `KEY_ENCRYPTION_KEY` it was taken
+under. Restoring it with the wrong key produces a database that looks intact
+and is not — every secret in it is silently unreadable until something tries
+to decrypt one.
+:::
+
 Restoring:
 
 ```bash
@@ -69,12 +92,13 @@ What it does **not** do is reconcile the world. After a restore:
 
 | What              | When                                                  |
 | ----------------- | ----------------------------------------------------- |
-| MongoDB dump      | Nightly, retained per your policy                     |
+| Backup            | Nightly, retained per your policy                     |
 | Environment file  | On change, held in a password manager or secret store |
 | Restore rehearsal | Occasionally, into a throwaway host                   |
 
 Rehearse a restore now and again. It is the step most often skipped, and the one
-that finds the problems.
+that finds the problems. See [Backup and restore](./backup-and-restore.md) for
+the drill, and for `verify`, which checks a backup is real without a restore.
 
 ## Cloud instances