Custom command container build steps ignore with configuration

## Atmos version

1.225.0

## Reproduction

A custom command in `.atmos.d/commands.yaml` contains a typed native container build step with `engine: buildx`, `context: app`, a tag, a `docker-container` driver, and registry `cache.from` / `cache.to` settings.

Run:

```bash
APP_IMAGE=example.invalid/demo:sha-test \
APP_IMAGE_CACHE=example.invalid/demo:buildcache \
ECR_REGISTRY=example.invalid \
atmos --use-version=1.225.0 build
```

With a logging `docker` shim first on `PATH`, Atmos invokes only:

```text
docker info
docker build -f Dockerfile .
```

It silently drops the configured Buildx engine, context, tag, driver, and cache settings.

## Expected

Custom commands should execute typed `container` steps through the native workflow container runner, preserving all `with:` settings. At a minimum, the resulting argv should contain `buildx`, the configured builder, `--cache-from`, `--cache-to`, tag, Dockerfile, and context.

## Impact

The feature build workflow calls `atmos build` and `atmos push`, so this silently uses Docker's default builder, misses the intended ECR cache, builds the wrong context, and does not tag the deterministic deployment image.

Start with the typed container step in `.atmos.d/commands.yaml` and reproduce `atmos --use-version=1.225.0 build` using the logging `docker` shim described in the issue. Trace how custom commands reach the native workflow container runner, then verify the resulting argv preserves `buildx`, the builder, cache settings, tag, Dockerfile, and context.

Written by the indexing model from the issue text.