feat: add Docker support and Gitea publish workflow

- Add a multi-stage Dockerfile for building and running the Go backend
- Add .dockerignore to optimize the Docker build context
- Create a Gitea Actions workflow to build and publish Docker images on tag push
- Register a new `/health` endpoint for container healthchecks
- Update README.md with Docker and Podman deployment instructions
- Ignore local `docker-compose.yml` in .gitignore

.gitignore

@@ -13,3 +13,4 @@ backend/static/uploads/*
 .env.*
 !.env.example
 scripts/env/dev.env
+docker-compose.yml