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]>

src/ui/localePicker.test.mjs

@@ -40,7 +40,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['ru', 'en', 'es', 'zh-CN', 'zh-Hant'],
+    ['ru', 'en', 'es', 'pt', 'zh-CN', 'zh-Hant'],
   );
   assert.deepEqual(
     codes(
@@ -50,7 +50,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['es', 'en', 'ru', 'zh-CN', 'zh-Hant'],
+    ['es', 'en', 'pt', 'ru', 'zh-CN', 'zh-Hant'],
   );
   assert.deepEqual(
     codes(
@@ -60,7 +60,7 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['en', 'es', 'ru', 'zh-CN', 'zh-Hant'],
+    ['en', 'es', 'pt', 'ru', 'zh-CN', 'zh-Hant'],
   );
   const rows = buildLocaleOptions({
     locales: MANY,