BoxShadow does not honor BorderRadius

### What happened?

### Relevant log output or stack trace

```shell

```

### Steps to reproduce

```bash
_new("Test") AUI_WITH_STYLE {
MinSize { 200_dp },
BorderRadius { 100_dp }
}
```

### Affected Platforms

Windows, Linux, macOS, Android, iOS, Emscripten

### Link to build, i.e. failing GitHub Action job (if any).

_No response_

Start by reproducing the AButton example with MinSize and BorderRadius, then trace the BoxShadow and BorderRadius rendering paths. Verify the result on the listed platforms and confirm that the shadow follows the rounded border rather than extending beyond it.

Written by the indexing model from the issue text.