30dc9d47

By: Michael Lynch <git@mtlynch.io>

Fix check-frontend nix build target to actually run checks

Use buildNpmPackage instead of mkBuildStep so npm deps are pre-fetched
in a fixed-output derivation rather than at build time (which fails
silently due to no network access in the Nix sandbox).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>