fix: disable inspect for non-previewable assets (#8989)

## Summary
Prevent text/other assets from opening a blank fullscreen viewer by
restricting inspect/zoom to previewable media kinds.

## Changes
- Add `isPreviewableMediaType` helper in shared `formatUtil`.
- Gate inspect/zoom actions in `AssetsSidebarTab`, `MediaAssetCard`, and
`MediaAssetContextMenu` using an allowlist (`image`, `video`, `audio`,
`3D`).
- Build gallery items from previewable assets only.
- Add unit tests for `isPreviewableMediaType`.

## Why
`ResultGallery` only renders image/video/audio; text/other assets could
previously enter fullscreen with no renderable content.

## Review Focus
- Verify text/other assets no longer show Inspect and do not open
fullscreen.
- Verify image/video/audio behavior is unchanged.
- Verify 3D still opens the 3D viewer dialog.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8989-fix-disable-inspect-for-non-previewable-assets-30c6d73d36508103a9b9da4fe50236ea)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Johnpaul Chiwetelu <49923152+Myestery@users.noreply.github.com>
Co-authored-by: GitHub Action <action@github.com>

packages/shared-frontend-utils/src/formatUtil.ts

@@ -583,3 +583,12 @@ export function getMediaTypeFromFilename(
 
   return 'other'
 }
+
+export function isPreviewableMediaType(mediaType: MediaType): boolean {
+  return (
+    mediaType === 'image' ||
+    mediaType === 'video' ||
+    mediaType === 'audio' ||
+    mediaType === '3D'
+  )
+}