Function getAnimationByIdWithFallback

Get animation by ID with category-based fallback

Implements a 3-tier fallback system:

1. Try direct ID lookup in ANIMATION_ID_REGISTRY
2. If not found, use category default from CATEGORY_DEFAULT_ANIMATIONS
3. If no category, use IDLE_STANCE as ultimate fallback

This function never returns undefined, making it safe for use in game logic.