fix(pt-br): migrate Hardhat tutorial to ethers v6

[vuyua9]

Summary

• Migrate the pt-br Hardhat tutorial to @nomicfoundation/hardhat-toolbox v4 and ethers v6 APIs.
• Replace deployed()/address with waitForDeployment()/target in the deploy script, test, and tutorial snippets.
• Make the Goerli configuration opt-in through environment variables so placeholder credentials do not break local Hardhat commands.
• Restore the ERC20 state declarations required by the existing constructor and mint/burn example.

Validation

• npm ci --ignore-scripts --no-audit --no-fund
• npx hardhat compile -> Compiled 2 Solidity files successfully
• npx hardhat test -> 1 passing
• git diff --check

Hardhat emitted warnings because the environment uses Node.js 22.22.0 and Solidity 0.8.34 is newer than its fully supported compiler range; compilation and the test still completed successfully.