This helps with items like "Living in Watermelon Foreground and Background", which has a species-specific foreground and bodyId=0 background.
With this flag set on the background, it won't appear for pets that don't _also_ have something else that fits. In this case, it hides it from Standard Vandas, and all non-standard colors.
There's some hacky limitations here: the item page still highlights the Vanda, even though clicking gives nothing; and the zone info for it is messy too, with the Background claiming to fit all species, and the LFI claiming to fit 54 specific species. But those don't seem important enough to code for!
I like making these more concise and consistent across the dropdown and the cards, I'm still not 100% sold on the design but it seems ok for now!
At first I had it in the dropdown as "Background (3)", but realized that conflicts with the usual pattern of like, saying how many items match a certain filter…
I think this will be generally useful to minimize switching around for common operations, but also I'm thinking of building a bulk assign tool for things with broken body IDs, and this will be the place for it to live, I think
