feat: add Farsi (fa) locale support

Add comprehensive Farsi translation for the webmail interface:
- Create locales/fa/common.json with Farsi translations
- Register 'fa' locale in i18n/routing.ts and i18n/request.ts
- Add Iran flag component (FlagIR) to flag-icons.tsx
- Add ف��رسی to language switcher dropdown
- Add Farsi language name to English locale for language selector

Translation covers login, sidebar, email viewer, composer, settings,
notifications, calendar, contacts, errors, shortcuts, and more.

i18n/request.ts

@@ -23,6 +23,9 @@ export default getRequestConfig(async ({ requestLocale }) => {
     case 'es':
       messages = (await import('../locales/es/common.json')).default;
       break;
+    case 'fa':
+      messages = (await import('../locales/fa/common.json')).default;
+      break;
     case 'fr':
       messages = (await import('../locales/fr/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', 'fr', 'hu', 'it', 'ja', 'ko', 'lv', 'nl', 'pl', 'pt', 'ro', 'ru', 'tr', 'uk', 'zh'] as const;
+const SUPPORTED_LOCALES = ['cs', 'da', 'de', 'en', 'es', 'fa', 'fr', 'hu', 'it', 'ja', 'ko', 'lv', 'nl', 'pl', 'pt', 'ro', 'ru', '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