fix(backup): kreisel/mukke/viadocu in db_user_for_container ergänzen

Diese drei Container failten still bei der DB-Enumeration (Default-User
`postgres` existiert dort nicht → `:list`-Fail), wurden also nie
gebackupt. Echte Superuser verifiziert: kreisel→kreisel (mana_kreisel),
mukke→mukke (mana_mukke), viadocu→viadocu (viadocu).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/mac-mini/backup-databases.sh

@@ -78,6 +78,9 @@ db_user_for_container() {
         pageta-postgres)           echo "pageta" ;;
         uload-postgres)            echo "uload" ;;
         comicello-postgres)        echo "comicello" ;;
+        kreisel-postgres)          echo "kreisel" ;;
+        mukke-postgres)            echo "mukke" ;;
+        viadocu-postgres)          echo "viadocu" ;;
         mana-infra-postgres)       echo "postgres" ;;
         *)                         echo "postgres" ;;
     esac