REFACTOR(secrets): flatten Vault paths

- Change secret paths from <category>/<app> to <app>
- databases/postgresql → postgresql
- databases/minio → minio
- databases/pgweb → pgweb
- cluster-infrastructure/velero → velero

postgresql/manifests/secret.yaml

@@ -19,7 +19,7 @@ spec:
   data:
     - secretKey: password
       remoteRef:
-        key: databases/postgresql
+        key: postgresql
         property: PASSWORD
 
 ---
@@ -44,5 +44,5 @@ spec:
   data:
     - secretKey: password
       remoteRef:
-        key: databases/postgresql
+        key: postgresql
         property: PASSWORD