Yarn-Stash gets a sheep

Replaced 13 cat mascot poses with 9 sheep poses. The cats were too close to Pusheen — close enough that someone on Reddit had already noted it. Sheep is on-theme anyway (the app is about yarn) and there's no ambiguity about who designed it.

Generated the whole sheep set from one Gemini render, then derived: app icon, splash screen, Android foreground/background/monochrome, favicon. Square-cropped from the top to dodge the watermark.

3 of the 9 poses are doing double-duty — sheep4 covers cat_lying, cat_reading_lg, and cat_sleeping_zzz for now. Will generate the missing 4 (sleeping, lying, standing, surprised) in the next pass.

Old cats are archived under assets/mascot/poses-old/ in case anyone misses them. Nobody will.