fix(pt-br): restore NFTSwap localized imports

[huyua9]

Summary

• restore the three Languages/pt-br/38_NFTSwap/NFTSwap.sol imports to the sibling localized ../34_ERC721/ directory
• keep the Portuguese NFTSwap tutorial self-contained with its localized ERC721 dependencies

Validation

• verified all three relative imports resolve to existing files
• git diff --check

This restores the import paths previously corrected in commit c6dbb1fc before the later Solidity version update reintroduced the root-relative paths.