i18n: add Portuguese Brazilian (Português) translation

[AugustoL]

Summary

Add Brazilian Portuguese language support to OpenScan.

Prerequisites

• feat: implement i18n infrastructure with react-i18next #130 (i18n infrastructure) must be completed first

Scope

Translate all user-facing strings to Brazilian Portuguese (Português Brasileiro), including:

• Navigation and common UI elements
• Address page content
• Block page content
• Transaction page content
• DevTools section
• Error messages
• Settings page

Files to create

src/locales/pt-BR/
  common.json
  address.json
  block.json
  transaction.json
  devtools.json
  errors.json
  network.json

Guidelines

• Use Brazilian Portuguese (pt-BR), not European Portuguese
• Keep technical blockchain terms in English where commonly used in Brazilian crypto community
• Maintain consistent terminology throughout
• Test all translations in context

Acceptance Criteria

• All translation files created
• All strings translated
• UI tested with Portuguese selected
• No truncation or layout issues
• Reviewed by native speaker (if possible)

Resources

• Portuguese blockchain terminology
• Base English files in src/locales/en/