docs(i18n): add Portuguese README translation

[obrenoalvim]

Summary

• Add docs/README.pt-BR.md, a Portuguese (pt-BR) translation of the root README, following the same structure as the existing translations (zh-CN, ja, de, fr, ko, ru)
• Add the Português entry to the language switcher in the root README and all six sibling translations

Changes

• docs/README.pt-BR.md: new Portuguese translation
• README.md, docs/README.{de,fr,ja,ko,ru,zh-CN}.md: language switcher updated with the Português link

Testing

• Docs-only change, no build/CI impact
• Diff shape matches the precedent Russian-translation PR (docs: add Russian README translation #1039): one new file plus a one-line switcher update in every existing README

[greptile-apps]

Confidence Score: 5/5

The documentation-only change appears safe to merge.

Summary

• Introduces docs/README.pt-BR.md with translated feature, installation, usage, licensing, and attribution documentation.
• Adds Português to the root README and all six existing translated README switchers.
• Preserves valid relative links and consistent navigation among all translations.

_{Reviews (1) · Last reviewed commit: "docs: add Portuguese README translation"}