Cycling backdrops reach a fallback path only once every rotating path
has failed to load, but every hero passed the rotation-agnostic backdrop
list as the rotation set and the aspect-ordered candidates as the
fallback. One servable wide backdrop was therefore enough to hide the
square background for good, so phone detail and Discover heroes
cover-fitted a 16:9 backdrop into a portrait box instead of showing the
square image Plex supplies.
Give the rotation set the same aspect-aware preference the candidate
list already has: near-square containers rotate the square background
alone and keep the backdrops behind it as fallbacks.
close#1700