Find image file for a card using Extended Title.
Images are stored in: <SETS_DIR>/<set_name>/<card_id>.png
- Parameters:
- extended_title
str Extended Title field (e.g., “Bayushi Kachiko • Experienced”)
- set_name
str Set name
- Returns:
- image_path
str or None Relative path like “sets/celestial_edition/card.png”, or None if not found