Container orchestration (Docker Compose / Kubernetes later)

Setup containerization using Docker for the entire application stack.

**Requirements:**
- Create Dockerfile for Node.js backend
- Create docker-compose.yml for multi-container setup (API, DB, Redis, etc.)
- Add .dockerignore file
- Configure environment-specific docker-compose files
- Add health checks in container configurations
- Document container setup and running instructions

**Deliverables:**
- Dockerfile for backend
- docker-compose.yml with all services
- .dockerignore file
- README with container setup instructions
- Verified builds and running containers