Allow reversible “mutual blocks” (show minimal entry + unblock button)

[juanseflash]

Problem: If support/admins create a block on behalf of a user while the other user already blocked them, the result is an unrecoverable mutual block — neither user can see the other or undo the block. This creates a “limbo” state.

Proposal: Allow mutual blocks to appear in each user's block list as a minimal entry (display only username and an action menu with “Unblock”), while preserving privacy (no playlists, followers, profile photo, etc.). This keeps privacy but allows users to undo mutual blocks when appropriate.

Rationale: Keeps user privacy intact while avoiding permanent edge-case lockouts introduced by admin actions. Other platforms implement similar flows. Please add support for this UX change.