fix(subsonic): pass playlistId in createPlaylist to update modification timestamp

[wzli]

Problem

When updating an existing playlist via the Subsonic REST API (createPlaylist?name=...), Explo does not pass the existing playlistId. Subsonic / Navidrome updates the tracklist internally, but does not update the playlist's changed modification timestamp in getPlaylists API responses.

Client applications that rely on delta sync (such as Symfonium, DSub, or Feishin) inspect the changed timestamp to determine if a playlist needs to be refreshed locally. Because the timestamp remained unchanged, clients continue to show the stale cached version offline.

Solution

1. Resolve the existing playlist ID via SearchPlaylist().
2. Pass playlistId=... parameter to createPlaylist when updating an existing playlist.

This signals Subsonic/Navidrome to update the target playlist directly and bump its changed timestamp so connected client apps detect and fetch the updated tracklist automatically.