Add Docker files

[Akshola00]

Description:

Create a Dockerfile and docker-compose.yml for running the app.

✅ Acceptance Criteria:

docker build -t axum-backend . builds the image

docker run -p 3000:3000 axum-backend starts the server

docker-compose up runs app + Postgres service

[fishonamos]

I will love to work on this

[Akshola00]

@fishonamos all yours