Latent preview of all batch items instead of just the first one

### Feature Idea

For image models, show a grid of all batch items instead of just the first batch item in the step-by-step previews, if enabled.

### Existing Solutions

My own local implementation which I'm submitting a PR for.

### Other

_No response_

Start by locating the step-by-step preview code and the setting that enables latent previews, then inspect how batch items are currently limited to the first item. Done means an enabled preview renders a grid containing every batch item for image models while existing behavior remains unchanged when disabled.

Written by the indexing model from the issue text.