refactored HTTP error handling and streamlined UI components by centralizing shared logic and removing redundant parameters

lib/api/errors/error_mapper.dart

@@ -6,6 +6,7 @@ import 'package:http/http.dart' as http;
 import 'package:nextcloud/nextcloud.dart';
 
 import '../api_error.dart';
+import '../http_errors.dart';
 import '../marianumcloud/talk/talk_error.dart';
 import 'app_exception.dart';
 import 'auth_exception.dart';
@@ -59,9 +60,8 @@ AppException? _dioToAppException(DioException error) {
 /// status plus a trimmed body preview (same format as the Talk API errors).
 AppException _dynamiteToAppException(DynamiteApiException error) {
   final status = error.statusCode;
-  final body = error.body.replaceAll(RegExp(r'\s+'), ' ').trim();
-  final preview = body.length > 500 ? '${body.substring(0, 500)}…' : body;
-  final detail = body.isEmpty ? 'HTTP $status' : 'HTTP $status body=$preview';
+  final preview = previewBody(error.body);
+  final detail = preview.isEmpty ? 'HTTP $status' : 'HTTP $status body=$preview';
   switch (status) {
     case 401:
       return AuthException.unauthorized(technicalDetails: detail);