Add localization support and translation script

- Introduced a new extension for localization in Flutter with `LocalizationExtension` in `l10n.dart`.
- Added a Python script `translate.py` for translating ARB/JSON localization files using a local Ollama model, preserving keys and placeholders, and handling ICU format rules.

lib/models/app_settings.dart

@@ -18,6 +18,7 @@ class AppSettings {
   final bool notifyOnNewAdvert;
   final bool autoRouteRotationEnabled;
   final String themeMode;
+  final String? languageOverride; // null = system default
   final bool appDebugLogEnabled;
   final Map<String, String> batteryChemistryByDeviceId;
 
@@ -39,6 +40,7 @@ class AppSettings {
     this.notifyOnNewAdvert = true,
     this.autoRouteRotationEnabled = false,
     this.themeMode = 'system',
+    this.languageOverride,
     this.appDebugLogEnabled = false,
     Map<String, String>? batteryChemistryByDeviceId,
   }) : batteryChemistryByDeviceId = batteryChemistryByDeviceId ?? {};
@@ -62,6 +64,7 @@ class AppSettings {
       'notify_on_new_advert': notifyOnNewAdvert,
       'auto_route_rotation_enabled': autoRouteRotationEnabled,
       'theme_mode': themeMode,
+      'language_override': languageOverride,
       'app_debug_log_enabled': appDebugLogEnabled,
       'battery_chemistry_by_device_id': batteryChemistryByDeviceId,
     };
@@ -89,6 +92,7 @@ class AppSettings {
       notifyOnNewAdvert: json['notify_on_new_advert'] as bool? ?? true,
       autoRouteRotationEnabled: json['auto_route_rotation_enabled'] as bool? ?? false,
       themeMode: json['theme_mode'] as String? ?? 'system',
+      languageOverride: json['language_override'] as String?,
       appDebugLogEnabled: json['app_debug_log_enabled'] as bool? ?? false,
       batteryChemistryByDeviceId: (json['battery_chemistry_by_device_id'] as Map?)?.map(
             (key, value) => MapEntry(key.toString(), value.toString()),
@@ -115,6 +119,7 @@ class AppSettings {
     bool? notifyOnNewAdvert,
     bool? autoRouteRotationEnabled,
     String? themeMode,
+    Object? languageOverride = _unset,
     bool? appDebugLogEnabled,
     Map<String, String>? batteryChemistryByDeviceId,
   }) {
@@ -138,6 +143,8 @@ class AppSettings {
       notifyOnNewAdvert: notifyOnNewAdvert ?? this.notifyOnNewAdvert,
       autoRouteRotationEnabled: autoRouteRotationEnabled ?? this.autoRouteRotationEnabled,
       themeMode: themeMode ?? this.themeMode,
+      languageOverride:
+          languageOverride == _unset ? this.languageOverride : languageOverride as String?,
       appDebugLogEnabled: appDebugLogEnabled ?? this.appDebugLogEnabled,
       batteryChemistryByDeviceId: batteryChemistryByDeviceId ?? this.batteryChemistryByDeviceId,
     );