Add procedural fart sound synthesis with physical modeling parameters: - sound.fart() API following bubble.mjs pattern - Fart class with pressure, pitch, rasp parameters - enableSustain/disableSustain for sustained sounds - fartflower.mjs piece: click button → flower blooms + fart sound Reusable across all pieces like bubble. Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>