feat(backend): AGI tutor RAG pipeline over course content (#406) - #482

buildx failed with: ERROR: failed to build: failed to solve: process "/bin/sh -c npm run build" did not complete successfully: exit code: 1

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/