Nix builds now require an explicit version = "..." in default.nix —
no implicit nixpkgs eval fallback. Also removes nettest (outgrown)
and updates all doc/task references.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Nix builds should resolve version from default.nix or nixpkgs only —
falling back to Dockerfile's CONTAINER_APP_VERSION masks real errors.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Merges build-container.yaml and build-container-nix.yaml into a single
workflow with a detect job that classifies containers by build type and
fans out to the correct runner. Containers with both Dockerfile and
default.nix get built on both runners.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>