i18n(de): complete and ship German

- Translate the remaining 1,868 strings in a neutral infinitive style (no
  Sie/du), with German compounds, decimal commas and CLDR one/other plurals.
- Review the #908 entries: knots are kn everywhere, the avionics codes BRG,
  CRS and DEST stay English like HDG and SPD, expand/collapse is
  ausklappen/einklappen, the radio toggle reads EIN/AUS, density SPARSE is
  DÜNN, the Thermal style is Wärmebild, German quotes in the shot prompt.
- Register de: catalog, LOCALES, LOCALE_NAMES (Deutsch), package boundaries,
  same-as-english (codes, product names, music genres, units).
- Tests: picker order and keyboard model with Deutsch, de/de-AT/de_CH
  normalization, browser de-DE resolves to German.
- docs/translations/de.md: style, plurals, units and glossary; TRANSLATORS.md
  and CURRENT-STATE.md list German.

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

src/i18n/i18n.test.mjs

@@ -34,6 +34,9 @@ test('normalizeLocale folds regional variants and rejects unshipped tags', () =>
   assert.equal(normalizeLocale('ru-RU'), 'ru');
   assert.equal(normalizeLocale(' RU '), 'ru');
   assert.equal(normalizeLocale('en_GB'), 'en');
+  assert.equal(normalizeLocale('de'), 'de');
+  assert.equal(normalizeLocale('de-AT'), 'de');
+  assert.equal(normalizeLocale('de_CH'), 'de');
   assert.equal(normalizeLocale('xx'), null);
   // Explicit script tags take precedence over regional defaults.
   assert.equal(normalizeLocale('zh'), 'zh-CN');
@@ -68,7 +71,7 @@ test('resolveLocale: ?lang= wins, then the stored choice, then browser languages
     resolveLocale({
       location: { search: '?lang=xx' },
       storage: memoryStorage(),
-      languages: ['de-DE', 'ru-RU'],
+      languages: ['ko-KR', 'ru-RU'],
     }),
     'ru',
   );
@@ -76,7 +79,15 @@ test('resolveLocale: ?lang= wins, then the stored choice, then browser languages
     resolveLocale({
       location: { search: '' },
       storage: memoryStorage(),
-      languages: ['de'],
+      languages: ['de-DE', 'ru-RU'],
+    }),
+    'de',
+  );
+  assert.equal(
+    resolveLocale({
+      location: { search: '' },
+      storage: memoryStorage(),
+      languages: ['ko'],
     }),
     'en',
   );