Function livestreamWithThumbnailPreview

livestreamWithThumbnailPreview(
    livestream: Livestream,
    userId: string,
    livestreamId: string,
): Promise<Livestream>
Attaches an ephemeral thumbnailPreviewUrl from R2 or a stored YouTube thumbnail URL.
Parameters
- livestream: Livestream
  Persisted livestream row.
- userId: string
  Owner user id.
- livestreamId: string
  Livestream row id.
Returns Promise<Livestream>
Livestream with optional preview URL for the editor UI.
- Defined in lib/livestreams/livestream-thumbnail-preview.ts:15