harden nextcloud backups: db dumps, alerting, drift fix

The data-only rsync left no way to restore a working instance: mysql/ and
config/ were never backed up, so a recovery would have files but no shares,
users or metadata. Dump the database before syncing files (a DB older than
the files is repairable with occ files:scan; a newer one references blobs
that never made it into the backup) and ship config/ alongside it.

Capture the --chmod=Du=rwx,Dgo=rx flag that had been hand-added to the
deployed skudak-cloud script. It was outside git, so every deploy silently
reverted it. It now lives in backup_rsync_extra_args.

Add OnFailure= alerting. The units failed silently before, which is how an
iDrive sync failure sat unnoticed since May. msmtp rather than the esmtp
already installed: the OpenSRS relay is port 465 (implicit TLS) and libesmtp
only speaks STARTTLS.

Exclude nextcloud.log* from the sync and cap log_rotate_size. skudak-cloud
was running at loglevel 0 and had written a 64 GB log that was being rsynced
and pushed to S3; set it to 2 to match the home instance.

Stagger the timers (04:00 / 04:30) so both finish before the 05:00 TrueNAS
snapshot task, and bound TimeoutStartSec so a wedged rsync cannot leave the
unit activating forever and skip every subsequent trigger.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ansible/roles/podman/tasks/containers/cloud-backup.yml

@@ -28,6 +28,27 @@
     mode: 0755
     setype: bin_t
 
+# Shared by every backup instance. Rendered once per include; the second and
+# later renders are no-ops.
+- name: template nextcloud backup alert script
+  become: true
+  ansible.builtin.template:
+    src: nextcloud/nextcloud-backup-alert.sh.j2
+    dest: /usr/local/bin/nextcloud-backup-alert.sh
+    owner: root
+    group: root
+    mode: 0755
+    setype: bin_t
+
+- name: template nextcloud backup failure handler unit
+  become: true
+  ansible.builtin.template:
+    src: nextcloud/nextcloud-backup-failed@.service.j2
+    dest: /etc/systemd/system/nextcloud-backup-failed@.service
+    owner: root
+    group: root
+    mode: 0644
+
 - name: template {{ backup_name }} backup systemd service
   become: true
   ansible.builtin.template: