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/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', 'de', 'en', 'es', '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', 'de', 'en', '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', 'de', 'es', 'ru', 'zh-CN', 'zh-Hant'],
   );
   const rows = buildLocaleOptions({
     locales: MANY,
@@ -95,6 +95,7 @@ test('each row gets the interface-language name for search, unless it only repea
   const byCode = Object.fromEntries(rows.map((row) => [row.code, row]));
   assert.equal(byCode.en.localName, 'английский');
   assert.equal(byCode.es.localName, 'испанский');
+  assert.equal(byCode.de.localName, 'немецкий');
   assert.equal(byCode.ru.localName, '', 'русский only repeats Русский');
   const english = buildLocaleOptions({
     locales: LOCALES,
@@ -261,7 +262,7 @@ test('keyboard model: open on the current language, move, choose, close', () =>
   model.openList();
   assert.equal(model.activeOption.code, 'ru');
   assert.deepEqual(model.keydown({ key: 'ArrowDown' }), { handled: true });
-  assert.equal(model.activeOption.code, 'en');
+  assert.equal(model.activeOption.code, 'de');
   model.keydown({ key: 'End' });
   assert.equal(model.activeOption.code, 'zh-Hant');
   model.keydown({ key: 'Home' });
@@ -275,7 +276,7 @@ test('keyboard model: open on the current language, move, choose, close', () =>
   model.keydown({ key: 'ArrowDown' });
   assert.deepEqual(model.keydown({ key: ' ' }), {
     handled: true,
-    choose: 'en',
+    choose: 'de',
   });
   assert.deepEqual(model.keydown({ key: 'Escape' }), {
     handled: true,