Fix: green background on diamond spritesheet
The original CodePen spritesheet PNG had a solid green background baked into every pixel — no alpha channel at all. The diamond sparkle content was drawn on top of green. When the spritesheet rendered on a non-green rarity color (legendary gold, mythic crimson, etc.), the green background showed through instead of the rarity color.
Fixed by processing the PNG to make all green-dominant pixels fully transparent, preserving only the diamond sparkle content (18% of pixels). The circle's rarity background color now shows through correctly behind the diamond animation.