The converter now falls back to using the source image_url from raw
data when image_file is not available (images not downloaded locally).
- Pokemon cards: use source image_url when image_file is null
- Trainer cards: same fallback behavior
- Regenerated all 382 card definitions with image URLs
Images point to pokemon-zone.com assets for now. When we host our
own images, cards with image_file will use our CDN instead.
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