feat(users): add getById API and UserBasicInfo

apps/lib/features/users/data/users_api.dart

@@ -1,12 +1,33 @@
 import 'package:social_app/core/api/i_api_client.dart';
 import 'models/user_response.dart';
 
+class UserBasicInfo {
+  final String id;
+  final String username;
+  final String? avatarUrl;
+
+  UserBasicInfo({required this.id, required this.username, this.avatarUrl});
+
+  factory UserBasicInfo.fromJson(Map<String, dynamic> json) {
+    return UserBasicInfo(
+      id: json['id'] as String,
+      username: json['username'] as String,
+      avatarUrl: json['avatar_url'] as String?,
+    );
+  }
+}
+
 class UsersApi {
   final IApiClient _client;
   static const _prefix = '/api/v1/users';
 
   UsersApi(this._client);
 
+  Future<UserBasicInfo> getById(String userId) async {
+    final response = await _client.get('$_prefix/$userId');
+    return UserBasicInfo.fromJson(response.data);
+  }
+
   Future<UserResponse> getMe() async {
     final response = await _client.get('$_prefix/me');
     return UserResponse.fromJson(response.data);