chore(deps): Bump actions/setup-node from 4 to 7 - #4

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, docker/build-push-action@v6, docker/setup-buildx-action@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

SecretsUsedInArgOrEnv: Do not use ARG or ENV instructions for sensitive data (ENV "JWT_SECRET") More info: https://docs.docker.com/go/dockerfile/rule/secrets-used-in-arg-or-env/