Dockerize the entire workflow

## Add Dockerfile(s)
### Minimal images:
- Python app image (base for producer, consumers, batch scripts)
- Optional separate Spark image to run Spark jobs via spark-submit (or use official Spark image with connector packages)
- Update/extend [docker-compose.yaml](vscode-file://vscode-app/opt/visual-studio-code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) to include:
- zookeeper (already present)
- kafka (already present — ensure advertised listeners work in compose)
- postgres

- Provide .env.example and documented env variables for secrets/config
- Provide a Makefile or bash helper scripts for common tasks