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/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', 'ar', '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', 'ru', 'ar', 'zh-CN', 'zh-Hant'],
   );
   assert.deepEqual(
     codes(
@@ -60,7 +60,17 @@ test('the current language comes first, the rest by their own names', () => {
         nativeNames: LOCALE_NAMES,
       }),
     ),
-    ['en', 'es', 'ru', 'zh-CN', 'zh-Hant'],
+    ['en', 'es', 'ru', 'ar', 'zh-CN', 'zh-Hant'],
+  );
+  assert.deepEqual(
+    codes(
+      buildLocaleOptions({
+        locales: LOCALES,
+        current: 'ar',
+        nativeNames: LOCALE_NAMES,
+      }),
+    ),
+    ['ar', 'en', 'es', 'ru', 'zh-CN', 'zh-Hant'],
   );
   const rows = buildLocaleOptions({
     locales: MANY,