🌐 Translate README to Portuguese (PT-BR)

[thidebrito]

Difficulty: good first issue
Time estimate: 1-2 hours

Translate the main README.md to Portuguese (PT-BR). Save as README.pt-BR.md.

Add a language switcher at the top of README.md:

> 🌍 Available in: [English (default)](README.md) · [Português](README.pt-BR.md)

Notes:

• Keep code blocks and command names in English
• Translate explanations, FAQs, headings
• Adapt examples to BR context where natural

PR welcome.