docs: sync Portuguese guide with English guide

[pullfrog]

Summary

• Bring docs/GUIDE.pt-BR.md up to date with the English guide's section structure and content.
• Add the missing desktop-layout, audio-output, and HDR/VRR troubleshooting sections.
• Add the missing package-download note to the build instructions and keep the existing pt-BR UI labels and links.

The English guide had no factual errors, so it was not changed.

Validation

• dotnet test tests/ConsoleMode.Tests/ConsoleMode.Tests.csproj — 133 passed.
• git diff --check — passed.
• The Windows-only app build was left to CI, as this environment is Linux.

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