migrate CI from GitHub Actions to Tangled Spindles
- Replace .github/workflows/CI.yml with .tangled/workflows/ci.yml
- Replace chrono with time crate to enable macOS cross-compilation from Linux
- All 4 targets build via napi cross-compile (-x / --use-napi-cross)
- cargo-zigbuild and cargo-xwin from nixpkgs (no cargo install needed)
- Publish on release/* branches only, uses TANGLED_REF_NAME for npm tag