temporary workaround for 500 error

**Root cause:**
The autogenerated Dart OpenAPI client (`UsersApi.createProfileImage()`) had two issues:
1. It set `Content-Type: multipart/form-data` without a boundary, which overrode the correct header that Dart's `MultipartRequest` would set (`multipart/form-data; boundary=...`).
2. It added the file to both `mp.fields` and `mp.files`, creating a duplicate text field.

**Result:**
Multer on the server failed to parse the multipart body, so `@UploadedFile()` was `undefined` → accessing `file.path` in `UserService.createProfileImage()` threw → **500 Internal Server Error**.

**Workaround:**
Bypass the autogenerated method in `UserApiRepository.createProfileImage()` and send the multipart request directly using the same `ApiClient` (basePath + auth), ensuring:
- No manual `Content-Type` header (let `MultipartRequest` set it with boundary)
- File only in `mp.files`, not `mp.fields`
- Proper filename fallback

mobile/lib/infrastructure/repositories/user_api.repository.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:http/http.dart';
@@ -18,8 +19,34 @@ class UserApiRepository extends ApiRepository {
   }
 
   Future<String> createProfileImage({required String name, required Uint8List data}) async {
-    final res = await checkNull(_api.createProfileImage(MultipartFile.fromBytes('file', data, filename: name)));
-    return res.profileImagePath;
+    // Workaround: the autogenerated OpenAPI client forces `Content-Type: multipart/form-data`
+    // without a boundary, which can break multer parsing server-side.
+    // We bypass `UsersApi.createProfileImage()` and send the multipart request directly,
+    // while still reusing the configured basePath + auth headers + http client.
+    final apiClient = _api.apiClient;
+
+    final headers = <String, String>{};
+    await apiClient.authentication?.applyToParams(<QueryParam>[], headers);
+    headers.addAll(apiClient.defaultHeaderMap);
+    headers.remove('Content-Type');
+    headers.remove('content-type');
+
+    final filename = name.isNotEmpty ? name : 'profile-picture.png';
+    final uri = Uri.parse('${apiClient.basePath}/users/profile-image');
+
+    final request = MultipartRequest('POST', uri)
+      ..headers.addAll(headers)
+      ..files.add(MultipartFile.fromBytes('file', data, filename: filename));
+
+    final streamed = await apiClient.client.send(request);
+    final response = await Response.fromStream(streamed);
+
+    if (response.statusCode >= 400) {
+      throw ApiException(response.statusCode, response.body);
+    }
+
+    final body = jsonDecode(response.body) as Map<String, dynamic>;
+    return body['profileImagePath'] as String;
   }
 
   Future<List<UserDto>> getAll() async {