fix(minio): freeze the community image by digest and alert on pull failure

MinIO deleted the community edition images upstream. Docker Hub reports
{"message":"object not found"} for minio/minio, and an anonymous pull of
quay.io/minio/mc returns HTTP 401. talos-cp-1 dropped the cached image during
the DiskPressure event on 2026-09-22. The tenant pod was recreated on
2026-09-23 and has been in ImagePullBackOff since. MinIO served no traffic for
13 days, which put vault-0 and loki-0 into CrashLoopBackOff and left the
paperless backups stuck.

Pin the tenant image to the digest of the last community release, so a retag or
a deletion on the mirror cannot break the pull again. Repoint the two
quay.io/minio/mc references at the archived Bitnami client image, also by
digest. Alert on ImagePullBackOff and on a pod that stays not ready, because
neither case raised any alert.

Evidence: https://hub.docker.com/v2/repositories/minio/minio/tags -> {"message":"object not found"}

k8s/apps/paperless/backup-cronjob.yaml

@@ -48,7 +48,7 @@ spec:
                   mountPath: /backup
           containers:
             - name: mc-mirror
-              image: quay.io/minio/mc:latest
+              image: docker.io/bitnamilegacy/minio-client:2025.7.21-debian-12-r3@sha256:73bd39f7899a0cef12b8dd5df13aa93a3ed1aaa44236542442e9ac76819ac158
               env:
                 - name: ACCESS_KEY
                   valueFrom: