Use a poster/thumbnail from a video file as the artwork for remote controls

If AVKit supports posters, we should use that as the "album art" for remote controls.
If it doesn't (or the current video file has no poster), we should select a frame from the video for that "album art". Probably 2% in or something like that.

- [ ] Investigate: Does AVKit support posters?
- [ ] If so, use a poster as the album art
- [ ] If no poster, auto-select a frame to use as the album art

Start by investigating whether AVKit supports poster artwork for remote controls, then inspect the existing remote-control artwork entry point in the media player. Verify the poster path and the fallback frame-selection path, including videos without posters; the work is done when remote controls show suitable artwork in both cases.

Written by the indexing model from the issue text.