feat: add Docker Compose deployment for MEAN stack

[Shivam-Infra-Labs]

What does this PR do?

This PR adds a Docker-based deployment workflow to the MEAN Stack Example application.

Changes

• Added Dockerfile for the Angular frontend
• Added NGINX configuration for static frontend serving and API reverse proxying
• Added Dockerfile for the Node.js/Express backend
• Added Docker Compose configuration for the application stack
• Added MongoDB container healthcheck
• Added persistent MongoDB volume
• Added multi-stage Docker builds
• Added .dockerignore files
• Added Docker architecture documentation
• Added Docker deployment documentation
• Added troubleshooting documentation

Verification

The application was tested locally using Docker Compose.

The following were verified:

• Angular frontend served successfully through NGINX
• Backend /healthcheck endpoint returned successfully
• Employee CRUD operations worked correctly
• MongoDB data persisted after container restart
• MongoDB data persisted after Docker Compose recreation

Notes

MongoDB 4.4 is currently used for this local learning environment. This version is old/EOL and is not intended as a production recommendation.

The Docker configuration is intended to provide a reproducible local containerized deployment workflow while keeping the existing application architecture intact.