Warn at startup when installed CRDs are stale or missing

The operator strict-decodes CR specs, so when the in-cluster CRDs lag the
running operator (e.g. CRDs pinned to v0.1.0 while the operator ran v0.3.0),
new spec fields fail to decode with no operator-side signal. This adds an
advisory startup check so the mismatch is visible in the operator logs.

- Add CheckCRDVersions: GET each owned CRD and verify it carries a
  version-sentinel spec field, logging a distinct WARNING per problem
  (missing CRD vs. present-but-stale schema); advisory only, never exits.
- Keep the sentinel list (buckets/managePolicy, objectstoreusers/
  retainOnDelete, bucketaccesses/rawStatements) in one place.
- Wire the check into operator startup after the manager config is available.
- Add apiextensions customresourcedefinitions get;list RBAC marker and
  regenerate config/rbac/role.yaml.
- Promote k8s.io/apiextensions-apiserver to a direct dependency.

Claude-Session: https://claude.ai/code/session_016CEncETbf8cvy1PhsHfFHM

config/rbac/role.yaml

@@ -16,6 +16,13 @@ rules:
   - patch
   - update
   - watch
+- apiGroups:
+  - apiextensions.k8s.io
+  resources:
+  - customresourcedefinitions
+  verbs:
+  - get
+  - list
 - apiGroups:
   - ceph.unkin.net
   resources: