Refactor MediaAssetViewModeToggle to use toggle-group component

## Context

The `MediaAssetViewModeToggle` component in `src/platform/assets/components/MediaAssetViewModeToggle.vue` was added in PR #7729. During review, it was noted that:

- The component overrides many button styles
- It's a single-use component, which we're trying to move away from

## Proposed Solution

Refactor this component to use the toggle-group component being introduced in PR #7767, which is based on [shadcn-vue's toggle-group](https://www.shadcn-vue.com/docs/components/toggle-group#single).

## References

- Original PR: #7729
- Comment thread: https://github.com/Comfy-Org/ComfyUI_frontend/pull/7729#discussion_r2663151326
- Toggle-group PR: #7767
- Requested by: @benceruleanlu

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-7863-Refactor-MediaAssetViewModeToggle-to-use-toggle-group-component-2e06d73d3650811f8187dba476c49f06) by [Unito](https://www.unito.io)