pick
fun pickStageSpotlightTileId(tiles: List<StageTile>, pinnedTile: StageTileKey?, contentPrimary: ResolvedContent?): String?
Resolve the spotlight (primary) tile id among the derived tiles.
A pinnedTile wins whenever its tile is still present (pin ANY tile, camera OR content). Click-to-unpin reverts to the default below.
Default spotlight = the MOST-RECENT active share, reusing the same primary chosen by pickPrimaryContent (contentPrimary) — surfaced as that owner's CONTENT tile.
Fallbacks (no pin, no content primary tile present): the first tile, then null when there are no tiles at all.