L-2: Dead existence check in tokenURI — ownerOf never returns address(0)

Summary

SoulboundProfileNFT.tokenURI checks if (ownerOf(tokenId) == address(0)) revert ERC721Metadata__URI_QueryFor_NonExistentToken(); — but ERC721.ownerOf reverts (ERC721NonexistentToken) for nonexistent/burned tokens; it never returns address(0). The branch is unreachable; the custom error can never fire. Harmless but misleading.