docs(readme): add Portuguese translation

[LaraGb]

Summary

• Added a Brazilian Portuguese README translation to improve accessibility for Portuguese-speaking users and teams.
• Helps increase adoption of RTK in Brazilian companies, where AI coding tools such as Claude and Copilot are rapidly expanding beyond engineering teams.
• Supports both developers and non-technical stakeholders (such as product managers and business teams) who are increasingly using AI tools to prototype ideas and collaborate more effectively with engineering teams.

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual review of translated documentation and markdown rendering

[CLAassistant]

All committers have signed the CLA.