Under prefers-reduced-motion the img rule sets transition:none, so
toggling opacity fires no transitionend and the handler that unmounts
the blurhash never ran. The placeholder stayed mounted for the life of
the component — visible in the letterbox bars wherever the cover is
rendered with fit="contain", and a live canvas per tile everywhere else.
One duration constant now drives both the CSS transition and the timer,
so they cannot drift.
c66ef971cf