Switch deployment pipeline from GitLab Agent kubectl to FluxCD image
automation. CI now only builds and pushes tagged images to Forgejo
registry; FluxCD detects new tags and updates the deployment manifest.
Fix Ecto.MultipleResultsError on /dashboard when a device has multiple
Preseem access point records by using limit(1) instead of Repo.get_by.
Replace inline cache with dedicated buildcache tag that stores all
intermediate builder layers. Unchanged stages like deps and compile
will be pulled from cache instead of rebuilt.
Add node:22-bookworm container image since ubuntu:latest lacks Node.js
required by JavaScript-based actions. Update checkout to v6 and
build-push-action to v6.
