Update db-backup-standalone.sh to use docker compose

- Replace docker service scale with docker compose stop/start
- Update service name from utility-bills-tracker_mongo to mongo
- Reference docker-compose-standalone.yaml compose file
- Update comments to reflect container operations vs swarm service

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

db-backup-standalone.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Configuration
+MONGO_SERVICE="mongo"
+COMPOSE_FILE="docker-compose-standalone.yaml"
+
+# stop mongo container while we copy its volume
+docker compose -f "$COMPOSE_FILE" stop "$MONGO_SERVICE"
+
+# timestamp for filename
+TIMESTAMP=$(date +"%Y-%m-%d-%H-%M")
+
+# backup directory and retention (can be overridden via env)
+BACKUP_DIR="${BACKUP_DIR:-backups}"
+KEEP="${KEEP:-7}"
+
+mkdir -p "$BACKUP_DIR"
+
+BACKUP_FILE="$BACKUP_DIR/mongo-volume-backup-$TIMESTAMP.tar.gz"
+
+sudo tar -czvpf "$BACKUP_FILE" mongo-volume
+
+# rotate old backups: keep only the newest $KEEP files
+if [ "$KEEP" -gt 0 ]; then
+  # gather files sorted newest-first
+  mapfile -t files < <(ls -1t "$BACKUP_DIR"/mongo-volume-backup-*.tar.gz 2>/dev/null || true)
+  if [ "${#files[@]}" -gt "$KEEP" ]; then
+    for f in "${files[@]:$KEEP}"; do
+      echo "Removing old backup: $f"
+      rm -f -- "$f"
+    done
+  fi
+fi
+
+# bring mongo container back up
+docker compose -f "$COMPOSE_FILE" start "$MONGO_SERVICE"