feat(wiki): nightly postgres backup + TOC on the right (#0048/#0050)

Add wikijs-backup, a nightly Borg CronJob (03:30) that dumps the Wiki.js postgres
DB to the Storage Box — the content lives in git-storage, but comments, local
accounts and the search index do not, so the runtime state gets its own backup.
Mirrors authentik-backup (DB-only), reusing synapse-backup-credentials and
-known-hosts with a separate repo path; NetworkPolicy lets the backup pod reach
wikijs-postgres. Also flip tocPosition to right so the page TOC sits beside the
content instead of in the left rail.

apps/production/networkpolicy.yaml

@@ -401,6 +401,10 @@ spec:
         - podSelector:
             matchLabels:
               app.kubernetes.io/name: wikijs
+        # Nächtliches Backup (wikijs-postgres-backup.yaml) braucht denselben DB-Zugang.
+        - podSelector:
+            matchLabels:
+              app.kubernetes.io/name: wikijs-backup
       ports:
         - protocol: TCP
           port: postgres