feat: Add Portuguese (Brazil) language support

[leozinhoszg]

• Add Portuguese translation file (pt/translation.json)
• Update i18n.js to include 'pt' in whitelist
• Add Portuguese option to SelectLanguage component
• Complete translation of all 1260 strings to Brazilian Portuguese

This contribution adds full support for Portuguese language, making OpenSign accessible to Brazilian Portuguese speakers.

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[leozinhoszg]

Hi maintainers! 👋

I've completed the Brazilian Portuguese translation for OpenSign. Here's what was done:

• ✅ All 1260 strings translated to Brazilian Portuguese
• ✅ Tested locally and language selector works correctly
• ✅ Lint checks passed successfully
• ✅ All placeholders preserved

I'm a native Brazilian Portuguese speaker and made sure to use appropriate business/formal language throughout.

Looking forward to your feedback! 🇧🇷

[iamlucas13]

LGTM

[Zathiel]

Hi @leozinhoszg

thanks for this PR

let me check with the team and come back to you !

Cheers

[Zathiel]

Dear @leozinhoszg

According to a call with the team will it be possible for you to compare the existing translation files with the one you create

Regards

[cozyClassic]

Dear @Zathiel
I'm trying to add Korean Language in this project,
I'm wondering how can I check the full-text when translation file worked, cause there are several word in translation.json file, not a full text.
Due the difference between grammar Korean and English, some words should might be checked in full-text.