Removed Media items remain visible due to playlist reference #1677

Describe the bug
Items from a disabled Media Folder remain visible in the interface after a full library rescan.

This appears to happen when an item from the Media Folder is referenced by a playlist. The playlist reference causes the track to remain available, but as a result the artist/album and related content also remain visible in the interface.

To Reproduce

• Start with a clean Lyrion configuration.
• Configure the following Docker volumes:
  • ${USERDIR:-$HOME}/temp/music:/music
  • ${USERDIR:-$HOME}/temp/music2:/music2
• Start Lyrion.
• Configure the default /music and /playlist folders.
• Go to Home → New Music.
• Select a random artist and random track.
• Right-click the track and save it to a playlist named item_on_music_folder.
• Go to Menu → Server → Basic Settings → Media Folders.
• Add /music2.
• Unselect /music.
• Select Rescan Media Library → Clear library and rescan everything.
• Save the settings and perform the requested rescan.

The result:

• Items from /music2 are available (as expected)
• The content from /music is removed from the library, except for the track that was added to the playlist.
• The artist/album associated with that track also remain visible in the interface.
• Removing /music completely from Media Folders and performing another Clear library and rescan everything does not remove the remaining track, artist, or album.
• Since /music no longer exists and Clear library and rescan everything was performed, this makes me suspect that the library is not actually being fully cleared.

Expected behavior
After disabling or removing a Media Folder and performing a full library rescan, content from that folder should no longer appear in the main library interface.

I found that the remaining track is referenced by a playlist, which appears to keep it available. However, this also causes the associated artist/album to remain visible, which is unexpected from a user's perspective.

It may be intentional for playlist items to remain available even when their original Media Folder is no longer configured, but there does not appear to be an obvious way to identify or remove these missing items from the playlists.

One possible solution would be an option such as "Clean playlists of missing items", or otherwise clearly indicating that the content is only available because it is referenced by a playlist.

System Information (please complete the following information):

• See compose file
• Firefox browser

services:
  lyrion-music-server:
    image: lmscommunity/lyrionmusicserver:9.1.2
    container_name: lyrion-music-server
    hostname: lyrion-music-server
    restart: unless-stopped
    network_mode: host
    volumes:
      - ${USERDIR:-$HOME}/temp/lyrion-music-server/config:/config
      - ${USERDIR:-$HOME}/temp/lyrion-music-server/playlist:/playlist
      - ${USERDIR:-$HOME}/temp/music:/music
      - ${USERDIR:-$HOME}/temp/music2:/music2
      - /etc/localtime:/etc/localtime:ro
    #ports:
    #  - 9000:9000/tcp
    #  - 9090:9090/tcp
    #  - 3483:3483/tcp
    #  - 3483:3483/udp
    user: root
    environment:
      - PUID=1000
      - PGID=1000
      - HTTP_PORT=9000
      - TZ=Europe/Amsterdam