Add database backup script with daily cron and 7-day retention

pg_dump-based backup script deployed alongside compose file. Deploy
script now installs a daily cron job (03:00) on Unraid automatically.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backup.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# ── Configuration ──────────────────────────────────────────────
+DEPLOY_DIR="/mnt/user/appdata/nuzlocke-tracker"
+BACKUP_DIR="${DEPLOY_DIR}/backups"
+RETENTION_DAYS=7
+DB_SERVICE="db"
+DB_NAME="nuzlocke"
+DB_USER="postgres"
+TIMESTAMP=$(date +%Y%m%d-%H%M%S)
+BACKUP_FILE="${BACKUP_DIR}/nuzlocke-${TIMESTAMP}.sql.gz"
+
+# ── Create backup directory ───────────────────────────────────
+mkdir -p "$BACKUP_DIR"
+
+# ── Dump database ─────────────────────────────────────────────
+cd "$DEPLOY_DIR"
+docker compose exec -T "$DB_SERVICE" pg_dump -U "$DB_USER" "$DB_NAME" | gzip > "$BACKUP_FILE"
+
+echo "Backup created: ${BACKUP_FILE}"
+
+# ── Rotate old backups ────────────────────────────────────────
+find "$BACKUP_DIR" -name "nuzlocke-*.sql.gz" -mtime +${RETENTION_DAYS} -delete
+
+REMAINING=$(find "$BACKUP_DIR" -name "nuzlocke-*.sql.gz" | wc -l)
+echo "Backups retained: ${REMAINING}"
+
+# ── Restore procedure ────────────────────────────────────────
+# To restore from a backup:
+#   cd /mnt/user/appdata/nuzlocke-tracker
+#   gunzip -c backups/nuzlocke-YYYYMMDD-HHMMSS.sql.gz | \
+#     docker compose exec -T db psql -U postgres nuzlocke