Title: Option to hide, remove, or replace song cover artwork

Users would like the ability to hide, delete, or replace the auto-generated cover artwork on a song within Songer.

Context: Some songwriters share the Songer version of a track for critique before distributing (e.g. via DistroKid), and feel the current auto-generated artwork doesn't always complement the song or leave the right impression. They'd like control over the cover, whether that means uploading their own image, or at minimum hiding/removing it when they plan to supply their own art later.

Key point raised by users: a blank cover is preferable to one that doesn't do the lyrics justice. The concern is strongest once a songwriter has locked in the exact version they want, since regenerating the track purely to cycle through cover variations isn't a viable workaround at that stage.

Prolific users are affected: one user reported publishing 100+ songs and routinely generating 15-20 artwork variations per track without landing a suitable one, reinforcing the need for a hide/remove option as a baseline, with upload/replace as the fuller solution.