Add Brazilian Portuguese (pt-BR) localization support

[ailtoneleveia]

Motivation

We are evaluating Buzz for adoption by Brazilian teams across desktop, mobile, and the new web experience. Conversations work well in Portuguese, but the English-only application chrome is an adoption barrier for non-technical users.

I would like to contribute Brazilian Portuguese (pt-BR) support and help maintain it as the interface evolves.

Proposed direction

I suggest an incremental, reviewable rollout:

1. Add the localization runtime with English as the source and fallback locale.
2. Detect the system/browser locale, with a persisted language override in Settings.
3. Extract one bounded surface first: navigation, onboarding, Messages, and their accessibility labels.
4. Add a human-reviewed pt-BR catalogue with key/interpolation parity tests.
5. Continue surface by surface instead of a repository-wide translation sweep.

The locale should use the BCP 47 tag pt-BR and display as Português (Brasil).

Prior art and coordination

The original block/buzz repository already has localization discussion in block/buzz#2929 and overlapping implementation attempts in block/buzz#5087, block/buzz#5152, and block/buzz#4250. I do not want to create another incompatible localization architecture.

Before turning the proposal into a ready-for-review implementation, could the maintainers clarify:

• Is block/buzz-app now the preferred target for new desktop/web localization work?
• Is react-i18next acceptable here, or would a repository-local message catalogue be preferred?
• Is an incremental first PR covering the main shell and Messages the desired review size?

Contribution commitment

I am willing to implement the infrastructure, provide the initial Brazilian Portuguese translation, test the complete user journey in Portuguese, and review terminology updates over time.