🎨 Add 42 new demo assets - Kai animations, zombies, buildings, terrain, environment

Generated assets (dual-style):
- Kai run animations (East/West, 16 frames)
- Kai portrait (neutral, 2 styles)
- Zombie walk/attack cycles (6 frames)
- Buildings: shack, campfire, well, chest (8 assets)
- Terrain: stone path, grass variation (4 tiles)
- Environment: oak tree, rock, bush, storage (10 objects)

Total: 42 new PNG files (21 base × 2 styles)
+ Batch generation scripts and manifests
+ Demo readiness checklist

scripts/organize_all_assets.py

@@ -230,7 +230,7 @@ def main():
     base_dir = Path('assets/images')
     
     # Skip these directories
-    skip_dirs = {'demo', 'demo_originals_with_white_bg'}
+    skip_dirs = {'demo_originals_with_white_bg'}
     
     total_organized = 0