i18n(pt): complete and ship Brazilian Portuguese

- Translate the remaining 1,868 strings (pt-BR, as in #909) and review the
  contributor entries: HUD codes BRG/SPD/RANGE stay as in the other
  languages, sentence-case layer and scene names, Space key named as on the
  keyboard, short PREV/NEXT/ON/OFF chips, and the CLDR many form (exact
  millions take «de») on every plural.
- Register pt: any pt tag (pt-BR, pt-PT) maps to it; the picker shows
  «Português (Brasil)».
- Codes, units and product names identical to English go to
  same-as-english.json.
- docs/translations/pt.md: style, plurals, units and glossary.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -3733,7 +3733,7 @@ test:track` 43 tracking invariants · headless QA harnesses under
 
 ### Interface localization (October 2026)
 
-Shipped locales: **en** (source and fallback), **es**, **ru**, **zh-CN** and **zh-Hant**. The code lives in
+Shipped locales: **en** (source and fallback), **es**, **pt** (Brazilian Portuguese), **ru**, **zh-CN** and **zh-Hant**. The code lives in
 `src/i18n/`. How to mark UI text: [`docs/I18N.md`](./I18N.md); translator workflow:
 [`docs/TRANSLATORS.md`](./TRANSLATORS.md).
 
@@ -3744,7 +3744,7 @@ Shipped locales: **en** (source and fallback), **es**, **ru**, **zh-CN** and **z
   value). English has no catalog; every other locale is
   `src/i18n/locales/<code>.json`, and a missing entry falls back to English.
 - **Locale choice.** `?lang=` → stored choice (`gev:locale:v1`) →
-  `navigator.languages` → English. Chinese tags default to `zh-CN`; Traditional Chinese tags
+  `navigator.languages` → English. Any `pt` tag (`pt-BR`, `pt-PT`) selects `pt`. Chinese tags default to `zh-CN`; Traditional Chinese tags
   select `zh-Hant`. Explicit `Hans` selects `zh-CN` regardless of region. `?lang=` is not stored, and share links drop
   it, so a recipient keeps their own language. The globe picker in the
   bottom-right corner (`src/ui/localePicker.js`) stores the choice, drops