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/ui/async_state_views.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import '../l10n/l10n.dart';
+
 class LoadingStateView extends StatelessWidget {
   final String? label;
 
@@ -83,7 +85,7 @@ class ErrorStateView extends StatelessWidget {
               const SizedBox(height: 12),
               OutlinedButton(
                 onPressed: onRetry,
-                child: const Text('Forsok igen'),
+                child: Text(context.l10n.retryAction),
               ),
             ],
           ],