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>

.gitea/workflows/deploy.yml

@@ -6,7 +6,7 @@ on:
       - main 
 
 env:
-  VERSION: 1.14.0
+  VERSION: 1.15.0
 
 jobs:
   # ЧАСТЬ 1: Собираем образы и кладем в Gitea (чтобы делиться с ребятами)