Model configuration:
- Add COMFYUI_MODELS_DIR for model pre-check (optional)
- Add ANIMATOOL_UNET_NAME, ANIMATOOL_CLIP_NAME, ANIMATOOL_VAE_NAME
- Add ANIMATOOL_CHECK_MODELS toggle
Model pre-check:
- Check if model files exist before generation
- Friendly error message with download link
- Skipped when COMFYUI_MODELS_DIR not set (remote ComfyUI)
Other improvements:
- Use config model names as defaults in _inject()
- Export DEFAULT_*_NAME constants