i18n(ar): register Arabic as the first right-to-left language

- Add ar to LOCALES (picker name العربية) and RTL_LOCALES, so <html dir>
  turns rtl; any ar-* tag maps to it.
- Intl formatters get ar-u-nu-latn: numbers and dates keep Western digits
  like the catalog, whatever the browser's ICU picks for Arabic regions.
- HUD quantities keep a space before an Arabic unit (2069.0 كم), as in
  Chinese, instead of running digits into the word.
- Codes and product names that stay Latin go to same-as-english.json.

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

src/i18n/ar-display.test.mjs

@@ -0,0 +1,101 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { formatDate, formatNumber, getLocale, setLocale, t, tn } from './index.js';
+import {
+  applyDocumentLanguage,
+  intlLocale,
+  LOCALE_STORAGE_KEY,
+  resolveLocale,
+} from './locale.js';
+import { hudQuantity, LOCALIZED_LOCALITY } from '../hudLocalityFormat.js';
+import { formatCockpitDistance } from '../ui/cockpitPresentation.js';
+import { READOUT_WORDS } from '../layers/recentImagery/display.js';
+
+test('Arabic resolves from URL, saved preference and browser language', () => {
+  assert.equal(
+    resolveLocale({
+      location: { search: '?lang=ar-EG' },
+      storage: { getItem: () => 'en' },
+      languages: ['en'],
+    }),
+    'ar',
+  );
+  assert.equal(
+    resolveLocale({
+      location: { search: '' },
+      storage: {
+        getItem: (key) => (key === LOCALE_STORAGE_KEY ? 'ar' : null),
+      },
+      languages: ['en'],
+    }),
+    'ar',
+  );
+  assert.equal(
+    resolveLocale({
+      location: { search: '' },
+      storage: { getItem: () => null },
+      languages: ['ar-SA', 'en'],
+    }),
+    'ar',
+  );
+});
+
+test('Arabic turns the page right-to-left; other languages stay left-to-right', () => {
+  const doc = { documentElement: {} };
+  applyDocumentLanguage(doc, 'ar');
+  assert.deepEqual(doc.documentElement, { lang: 'ar', dir: 'rtl' });
+  applyDocumentLanguage(doc, 'zh-CN');
+  assert.deepEqual(doc.documentElement, { lang: 'zh-CN', dir: 'ltr' });
+});
+
+test('Arabic formats with Western digits whatever ICU defaults to', () => {
+  assert.equal(intlLocale('ar'), 'ar-u-nu-latn');
+  assert.equal(intlLocale('ru'), 'ru');
+  const previous = getLocale();
+  try {
+    setLocale('ar');
+    assert.equal(formatNumber(1234.5), '1,234.5');
+    assert.equal(
+      formatDate(Date.UTC(2026, 7, 26), {
+        day: 'numeric',
+        month: 'long',
+        year: 'numeric',
+        timeZone: 'UTC',
+      }),
+      '26 أغسطس 2026',
+    );
+    assert.doesNotMatch(formatNumber(9876543210), /[٠-٩]/);
+  } finally {
+    setLocale(previous);
+  }
+});
+
+test('Arabic uses all six plural forms and spaced HUD units', () => {
+  const previous = getLocale();
+  try {
+    setLocale('ar');
+    assert.deepEqual(
+      [0, 1, 2, 3, 11, 100].map((n) =>
+        tn(n, '{count} SOURCE', '{count} SOURCES'),
+      ),
+      [
+        '0 مصدر',
+        'مصدر واحد (1)',
+        'مصدران (2)',
+        '3 مصادر',
+        '11 مصدرًا',
+        '100 مصدر',
+      ],
+    );
+    assert.equal(hudQuantity(2069, 'km', 1), '2069.0 كم');
+    assert.equal(formatCockpitDistance(14000), '14 كم');
+    assert.equal(
+      LOCALIZED_LOCALITY.sector({ latDeg: 21.33, lonDeg: -77.5 }),
+      'القطاع 21.33ش 77.50غ',
+    );
+    assert.equal(READOUT_WORDS.daysAgo(9), 'قبل 9 أيام');
+    assert.equal(t('SAVE KEYS'), 'حفظ المفاتيح');
+  } finally {
+    setLocale(previous);
+  }
+});