AI-powered upgrade to POST /v1/cards/image-search. Where image-search returns a ranked list of visually similar candidates, image-match uses AI to pick the single best_match card and resolve its color/finish variant (e.g. Base vs. Silver vs. Red).

Returns best_match (null when the AI isn't confident) plus the candidates it considered, so callers can fall back to the ranked list when the match is uncertain. The best match and every candidate carry the card's prices section (grade/price pairs, one per grade), so a caller can show a price without a second request.

{
  "image_url": "https://example.com/card.jpg",
  "k": 10
}