feat(i18n): add full Arabic (ar) translation

Adds a complete Arabic locale (2759 keys, full parity with en) and wires
it into routing, RTL direction detection, message loading, the language
switcher, and flag icons alongside the existing he/fa RTL locales.

i18n/direction.ts

@@ -1,5 +1,5 @@
-// RTL locales: Hebrew (he) and Persian/Farsi (fa). Everything else is LTR.
-const rtlLocales = new Set(['he', 'fa']);
+// RTL locales: Arabic (ar), Hebrew (he), and Persian/Farsi (fa). Everything else is LTR.
+const rtlLocales = new Set(['ar', 'he', 'fa']);
 
 export function getLocaleDirection(locale: string): 'ltr' | 'rtl' {
   return rtlLocales.has(locale) ? 'rtl' : 'ltr';

i18n/request.ts

@@ -33,6 +33,9 @@ export default getRequestConfig(async ({ requestLocale }) => {
   // Use static imports for better compatibility
   let messages;
   switch (locale) {
+    case 'ar':
+      messages = (await import('../locales/ar/common.json')).default;
+      break;
     case 'cs':
       messages = (await import('../locales/cs/common.json')).default;
       break;

i18n/routing.ts

@@ -12,7 +12,7 @@ const localePrefix = (process.env.NEXT_PUBLIC_LOCALE_PREFIX ?? 'never') as
   | 'always'
   | 'as-needed';
 
-const SUPPORTED_LOCALES = ['cs', 'da', 'de', 'en', 'es', 'fa', 'fr', 'he', 'hu', 'it', 'ja', 'ko', 'lv', 'nl', 'pl', 'pt', 'ro', 'ru', 'sk', 'tr', 'uk', 'zh'] as const;
+const SUPPORTED_LOCALES = ['ar', 'cs', 'da', 'de', 'en', 'es', 'fa', 'fr', 'he', 'hu', 'it', 'ja', 'ko', 'lv', 'nl', 'pl', 'pt', 'ro', 'ru', 'sk', 'tr', 'uk', 'zh'] as const;
 
 // Fallback locale used when the visitor's Accept-Language header does not
 // match any supported locale (and no NEXT_LOCALE cookie is set yet). Admins