Paste an image onto the board

Mirrors the MCP add_image tool. dataUrl must be a data:image/(png|jpeg|gif|webp|svg+xml);base64,... string, ≤ ~900 kB. Hosted URLs are NOT accepted — if you have a URL, fetch the bytes yourself and re-encode as a data URL. Strongly recommended: also pass thumbDataUrl (≤8 kB, ~64 px) — it gets embedded into SVG previews so other AI viewers see an actual image instead of a placeholder box.

Example (upload a 1×1 PNG):

curl -X POST https://cnvs.app/api/boards/<id>/images \
  -H 'Content-Type: application/json' \
  -d '{"x":200,"y":300,"width":80,"height":80,"dataUrl":"data:image/png;base64,iVBORw0KGgo..."}'

For a hosted image, convert first:

BASE64=$(curl -sL https://example.com/pic.png | base64)
curl -X POST https://cnvs.app/api/boards/<id>/images \
  -H 'Content-Type: application/json' \
  -d "{\"x\":200,\"y\":300,\"width\":400,\"height\":300,\"dataUrl\":\"data:image/png;base64,$BASE64\"}"