feat: Add Docker support for easy distribution

- Multi-stage Dockerfile for minimal image size (~119MB)
- Includes PostgreSQL, MySQL, MariaDB client tools
- Non-root user (UID 1000) for security
- Docker Compose examples for all use cases
- Complete Docker documentation (DOCKER.md)
- Kubernetes CronJob examples
- Support for Docker secrets
- Multi-platform build support

Docker makes deployment trivial:
- No dependency installation needed
- Consistent environment
- Easy CI/CD integration
- Kubernetes-ready

.dockerignore

@@ -0,0 +1,21 @@
+.git
+.gitignore
+*.dump
+*.dump.gz
+*.sql
+*.sql.gz
+*.tar.gz
+*.sha256
+*.info
+.dbbackup.conf
+backups/
+test_workspace/
+bin/
+dbbackup
+dbbackup_*
+*.log
+.vscode/
+.idea/
+*.swp
+*.swo
+*~