Pin openbao secrets plugins to exact versions (#492)

## Why

`ensure: present`/`latest` lets the plugin binaries drift from the sha256 pinned in the terraform-vault catalog (`config/plugins/*.yaml`). On the next OpenBao restart, a drifted binary fails the sha check and the plugin won't launch — a latent footgun (hit exactly this with rancher on `ensure: latest`).

## Changes

Pin each secrets plugin to the version whose binary matches its registered catalog sha (all verified against the RPMs in rpm-internal):

- `openbao-plugin-secrets-litellm`: **0.1.1** (sha 2263ebcb…)
- `openbao-plugin-secrets-gpg`: **0.1.0** (sha 0e92d740…)
- `openbao-plugin-secrets-rancher`: **0.1.1** (sha 9e597cd9…; was `ensure: latest`)

All three are no-op on the binary (installed versions already match) — this just locks them so a future release can't silently upgrade the binary out of lockstep with the catalog.

`openbao-plugins` (base bundle) left unpinned — its version couldn't be verified from the tooling side and it tracks the openbao package, not a catalog sha.

## Note

To upgrade a plugin in future: bump the RPM version here **and** the catalog sha256 in terraform-vault in the same change, then `vault write sys/plugins/reload/backend plugin=<name>`.

---------

Co-authored-by: Ben Vincent <neotheo@gmail.com>
Reviewed-on: #492
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

hieradata/roles/infra/storage/vault.yaml

@@ -27,8 +27,14 @@ profiles::nginx::simpleproxy::proxy_port: 8200
 profiles::nginx::simpleproxy::proxy_path: '/'
 
 profiles::packages::include:
+  # openbao-plugins (base bundle) left unpinned; it tracks the openbao package.
   openbao-plugins: {}
-  openbao-plugin-secrets-litellm: {}
-  openbao-plugin-secrets-gpg: {}
+  # Secrets plugins pinned to the exact version whose binary matches the sha256
+  # registered in terraform-vault (config/plugins/*.yaml). Bump both in lockstep
+  # on upgrade, or OpenBao refuses to launch the plugin after a restart.
+  openbao-plugin-secrets-litellm:
+    ensure: '0.1.1'
+  openbao-plugin-secrets-gpg:
+    ensure: '0.1.0'
   openbao-plugin-secrets-rancher:
-    ensure: latest
+    ensure: '0.1.1'