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

README.md

@@ -16,6 +16,31 @@ Professional database backup and restore utility for PostgreSQL, MySQL, and Mari
 
 ## Installation
 
+### Docker (Recommended)
+
+**Pull from registry:**
+```bash
+docker pull git.uuxo.net/uuxo/dbbackup:latest
+```
+
+**Quick start:**
+```bash
+# PostgreSQL backup
+docker run --rm \
+  -v $(pwd)/backups:/backups \
+  -e PGHOST=your-host \
+  -e PGUSER=postgres \
+  -e PGPASSWORD=secret \
+  git.uuxo.net/uuxo/dbbackup:latest backup single mydb
+
+# Interactive mode
+docker run --rm -it \
+  -v $(pwd)/backups:/backups \
+  git.uuxo.net/uuxo/dbbackup:latest interactive
+```
+
+See [DOCKER.md](DOCKER.md) for complete Docker documentation.
+
 ### Download Pre-compiled Binary
 
 Linux x86_64: