Creator ruling: the Scoreboard layer exists in every scene rather than being added five times.
ScoreboardHealer.Ensure keeps exactly one per scene — healed on load like the Background and Brand
logo — so a scene can never end up with two, and 'off' is the ordinary per-scene eye toggle rather
than a delete.
It is appended as the TOPMOST layer on purpose: a full-width strip draws over the scene, and
inserting it above the background would break the Brand logo's documented invariant (directly above
the background). That choice is also why the layer-reorder test still passes untouched.
Also: a layer-list icon for the type, so the row is not blank.
Guard: ScoreboardHealerTests — one per scene, topmost, exact strip geometry, idempotent, and a
duplicate healed back to one.
