Build & Deploy (Nix) / build-and-deploy (push) Failing after 7s
The Gitea Actions runner image (docker.gitea.com/runner-images:ubuntu-latest)
does not have Nix pre-installed, causing 'nix: command not found' on the
build step.
Add an 'Install Nix' step using the Determinate Systems installer
(--no-daemon mode since the runner runs in a container).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>