ui(i18n): add Brazilian Portuguese translation

[eduardomozart]

Description

This PR introduces full Brazilian Portuguese (pt-BR) translation support for the application UI.

Related Issue

Closes #

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🌍 Translation (new language or translation update)
• 🔧 Refactoring (code change that neither fixes a bug nor adds a feature)
• 🧪 Tests (adding or updating tests)

Changes Made

• Added full Brazilian Portuguese translation files for the application (resources/i18n/pt-BR/main.json, rclone.json, and rclone-providers.json).
• Translated README.pt-BR.md into natural Brazilian Portuguese and updated language switcher links across all localized README files (en-US, es-ES, fr-FR, tr-TR, zh-CN).
• Registered the pt-BR locale in the backend settings schema (src-tauri/src/core/settings/schema.rs) and frontend cron locale mapper (src/app/services/i18n/cron-locale.mapper.ts).

Testing Performed

• Tested on Linux
• Tested on macOS
• Tested on Windows
• Tested in development mode (npm run tauri dev)

Screenshots

Checklist

• My code follows the project's code style
• I have run npm run lint:all and fixed any issues
• I have updated the documentation if needed
• My changes don't introduce any new warnings
• I have tested my changes thoroughly

Additional Notes

All translations have been carefully adapted to standard Brazilian Portuguese terms used in file management and cloud synchronization while preserving formatting, shields, and Markdown structure.

[Hakanbaban53]

Thanks for adding the Brazilian Portuguese translation! Looks good, approving.

Checks are failing, but this looks like it's related to the same pre-existing librclone mobile issue I mentioned earlier, unrelated to your changes, so I'll bypass and merge.