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>

compose.yaml

@@ -16,8 +16,30 @@ services:
       timeout: 3s
       retries: 10
 
+  db-backup:
+    image: postgres:17-alpine
+    restart: unless-stopped
+    depends_on:
+      db:
+        condition: service_healthy
+    environment:
+      POSTGRES_USER: gmrelay
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:?Set POSTGRES_PASSWORD in .env}
+      POSTGRES_DB: gmrelay_db
+      PGPASSWORD: ${POSTGRES_PASSWORD:?Set POSTGRES_PASSWORD in .env}
+      BACKUP_RETENTION_DAYS: ${BACKUP_RETENTION_DAYS:-7}
+    volumes:
+      - pgbackups:/backups
+    networks:
+      - gmrelay
+    entrypoint: ["sh", "-c"]
+    command:
+      - |
+        echo "0 3 * * * pg_dump -h db -U gmrelay -d gmrelay_db | gzip > /backups/gmrelay_db_\$$(date +\%Y\%m\%d_\%H\%M\%S).sql.gz && find /backups -name 'gmrelay_db_*.sql.gz' -type f -mtime +\$${BACKUP_RETENTION_DAYS} -delete" | crontab -
+        crond -f
+
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:1.14.0
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:1.15.0
     restart: always
     depends_on:
       db:
@@ -30,7 +52,7 @@ services:
       - gmrelay
 
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:1.14.0
+    image: git.codeanddice.ru/toutsu/gmrelay-web:1.15.0
     restart: always
     depends_on:
       db:
@@ -52,6 +74,8 @@ volumes:
     name: ${POSTGRES_VOLUME_NAME:-game_pgdata}
   web_keys:
     name: ${WEB_KEYS_VOLUME_NAME:-gmrelay_web_keys}
+  pgbackups:
+    name: ${BACKUP_VOLUME_NAME:-game_pgbackups}
 
 networks:
   gmrelay: