Docker FROM scratch returns "Image scratch is not an ECR Image"

### Product Version

- [ ] Amazon SageMaker Studio Classic
- [x] Amazon SageMaker Studio
- [ ] Issue is not related to SageMaker Studio

### Issue Description

I am trying to build a Docker Container within Sagemaker Studio AI starting from scratch. I have enabled Docker for the Domain.

Simplest example:
```
FROM scratch

RUN echo "Hello"
```

### Expected Behavior

I would expect that scratch would be treated as a special case as according to documentation I don't see anyway to bring it into ECR:

```
While scratch appears in Docker’s repository on the hub, you can’t pull it, run it, or tag any image with the name scratch. Instead, you can refer to it in your Dockerfile. For example, to create a minimal container using scratch
```

### Observed Behavior

`{"message":"Forbidden. Reason: [ValidateVPCOnlyModeImage] Image scratch is not an ECR Image. Studio VPC Only Mode allows Amazon ECR private registry Images belonging to trusted AWS Account IDs configured in Studio Domain API Settings"}`

### Product Category

Code-Editor

### Feedback Category

Configuration and Setup

### Other Details

_No response_

The issue provides no repository files, tests, or implementation entry points. Start by reproducing the minimal Dockerfile with `FROM scratch` in SageMaker Studio with Docker enabled, then trace the VPC-only image validation; done means this special base is accepted without the reported ECR-image error.

Written by the indexing model from the issue text.