Refactor voice support and add Greek localization

- Updated voice support to only include iOS, removing MacOS support.
- Added Greek (el) to the list of supported locales in LocalePreferences.
- Enhanced localization strings for Greek language.
- Modified Podfile to exclude C source files from the macOS build of codec2_flutter, as voice messages are iOS-only.

lib/l10n/app_localizations.dart

@@ -6,6 +6,7 @@ import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:intl/intl.dart' as intl;
 
 import 'app_localizations_de.dart';
+import 'app_localizations_el.dart';
 import 'app_localizations_en.dart';
 import 'app_localizations_es.dart';
 import 'app_localizations_fr.dart';
@@ -100,6 +101,7 @@ abstract class AppLocalizations {
   /// A list of this localizations delegate's supported locales.
   static const List<Locale> supportedLocales = <Locale>[
     Locale('de'),
+    Locale('el'),
     Locale('en'),
     Locale('es'),
     Locale('fr'),
@@ -4066,6 +4068,7 @@ class _AppLocalizationsDelegate
   @override
   bool isSupported(Locale locale) => <String>[
     'de',
+    'el',
     'en',
     'es',
     'fr',
@@ -4083,6 +4086,8 @@ AppLocalizations lookupAppLocalizations(Locale locale) {
   switch (locale.languageCode) {
     case 'de':
       return AppLocalizationsDe();
+    case 'el':
+      return AppLocalizationsEl();
     case 'en':
       return AppLocalizationsEn();
     case 'es':