infra: add PostgreSQL daily backup via pg_dump with rotation

- Add db-backup service to compose.yaml (postgres:17-alpine + cron)
- Add pgbackups volume for backup storage
- Add scripts/restore.sh for manual restore from latest backup
- Update .env.example with BACKUP_RETENTION_DAYS and BACKUP_VOLUME_NAME
- Document backup/restore flow in README

Bump version -> 1.15.0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/restore.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+# GM-Relay PostgreSQL Backup Restore Script
+# Usage: ./scripts/restore.sh [backup_file]
+# If no file is provided, uses the most recent backup.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+# Check required env
+if [ -z "${POSTGRES_PASSWORD:-}" ]; then
+    if [ -f "${PROJECT_ROOT}/.env" ]; then
+        export $(grep -v '^#' "${PROJECT_ROOT}/.env" | xargs) 2>/dev/null || true
+    fi
+fi
+
+if [ -z "${POSTGRES_PASSWORD:-}" ]; then
+    echo "ERROR: POSTGRES_PASSWORD is not set. Please set it in your environment or .env file."
+    exit 1
+fi
+
+BACKUP_DIR="${PROJECT_ROOT}/backups"
+
+# Determine backup file
+if [ $# -ge 1 ]; then
+    BACKUP_FILE="$1"
+else
+    BACKUP_FILE=$(find "${BACKUP_DIR}" -name 'gmrelay_db_*.sql.gz' -type f -printf '%T+ %p\n' 2>/dev/null | sort -r | head -n1 | cut -d' ' -f2-)
+    if [ -z "${BACKUP_FILE}" ]; then
+        echo "ERROR: No backup files found in ${BACKUP_DIR}."
+        exit 1
+    fi
+fi
+
+if [ ! -f "${BACKUP_FILE}" ]; then
+    echo "ERROR: Backup file not found: ${BACKUP_FILE}"
+    exit 1
+fi
+
+echo "=================================================="
+echo "  GM-Relay PostgreSQL Restore"
+echo "=================================================="
+echo ""
+echo "Backup file: ${BACKUP_FILE}"
+echo "Database:    gmrelay_db"
+echo "User:        gmrelay"
+echo ""
+read -p "This will OVERWRITE the current database. Are you sure? [y/N] " CONFIRM
+
+if [[ ! "${CONFIRM}" =~ ^[Yy]$ ]]; then
+    echo "Restore cancelled."
+    exit 0
+fi
+
+echo ""
+echo "Restoring database from ${BACKUP_FILE}..."
+
+# Restore using docker compose exec to leverage the running postgres container
+docker compose -f "${PROJECT_ROOT}/compose.yaml" exec -T db psql \
+    -U gmrelay \
+    -d gmrelay_db \
+    -c "DROP SCHEMA public CASCADE; CREATE SCHEMA public;" 2>/dev/null || true
+
+gunzip -c "${BACKUP_FILE}" | docker compose -f "${PROJECT_ROOT}/compose.yaml" exec -T db psql \
+    -U gmrelay \
+    -d gmrelay_db
+
+echo ""
+echo "=================================================="
+echo "  Restore completed successfully!"
+echo "=================================================="