feat(localization): Implement Swedish localization and error messages

- Added localization support for Swedish and English languages.
- Integrated localized strings for user messages in the API error mapper.
- Updated UI components to use localized strings for labels and messages.
- Ensured all error messages are context-aware and utilize the localization framework.
- Created regression test to prevent common ASCII fallbacks in Swedish UI text.

flutter/lib/core/api/api_error_mapper.dart

@@ -1,21 +1,23 @@
+import 'package:flutter/widgets.dart';
+
+import '../l10n/l10n.dart';
 import 'api_exception.dart';
 
-String mapErrorToUserMessage(Object error) {
+String mapErrorToUserMessage(Object error, BuildContext context) {
+  final l10n = context.l10n;
   if (error is ApiException) {
     switch (error.type) {
       case ApiErrorType.unauthorized:
-        return 'Din session har gatt ut. Logga in igen.';
+        return l10n.sessionExpiredError;
       case ApiErrorType.forbidden:
-        return 'Du saknar behorighet for denna funktion.';
+        return l10n.forbiddenError;
       case ApiErrorType.server:
-        return 'Serverfel uppstod. Forsok igen om en stund.';
+        return l10n.serverError;
       case ApiErrorType.network:
-        return 'Natverksfel. Kontrollera anslutningen och forsok igen.';
+        return l10n.networkError;
       case ApiErrorType.unknown:
-        return error.message.isNotEmpty
-            ? error.message
-            : 'Ett ovantat fel uppstod.';
+        return error.message.isNotEmpty ? error.message : l10n.unexpectedError;
     }
   }
-  return 'Ett ovantat fel uppstod.';
+  return l10n.unexpectedError;
 }