fix NFT page layout to prevent image size change

[yushih]

Task: https://emurgo.atlassian.net/browse/YW-332

---

Note

Improves NFT image rendering to prevent layout shifts and maintain consistent sizing.

• Extends NftImage with fillBox (controls objectFit: cover|contain) and contentWidth; passes width/height to fallback SvgWrapper
• Updates NftCard to use fillBox=true so thumbnails fill their containers
• Refactors NftDetails image area: fixed container (max 550px, 550px height), centered content, and Grid aligned to flex-start for stable layout
• Minor structural tweaks (wrap root in Box) and size props passed to NftImage for modal/details views

^{Written by Cursor Bugbot for commit d8f8045. This will update automatically on new commits. Configure here.}