feat(docs): Brazilian Portuguese (pt-br) translations

[vishr]

What

Adds Brazilian Portuguese (pt-br) as a fifth locale, alongside English, 简体中文, 日本語, and Español. Full translation pass of Guide, Middleware, and Cookbook (59 docs), done via Codex.

Changes

• astro.config.mjs — register the pt-br locale ({ label: 'Português', lang: 'pt-BR' }) and add pt-BR sidebar group-label translations (Guia / Middleware / Receitas).
• src/content/docs/pt-br/** — 59 translated docs mirroring the en structure (14 guide, 25 middleware, 20 cookbook).

Notes / verification

• The branch predated the Spanish PR (feat(docs): Spanish (es) translations #414), so I merged current master in and resolved the astro.config.mjs conflict — all five locales now coexist (en / zh-cn / ja / es / pt-br), and the es content is preserved.
• Sidebar pt-BR translation key correctly uses the BCP-47 lang tag (matching lang: 'pt-BR'), consistent with the zh-CN convention.
• Production build passes: 301 pages, including 60 pt-br/ HTML pages.
• Integrity checks: all code fences balanced, no un-localized internal links, no blank descriptions, frontmatter translated.

🤖 Generated with Claude Code