Add user creation functionality: implement API endpoint for creating new users, including request handling and response management. Update frontend to support user creation with a new form in the UsersPanel, integrating role selection and input validation. Enhance i18n for new user-related strings.

backend/src/TeleWave.Application/Admin/Users/CreateUser/CreateUserCommand.cs

@@ -0,0 +1,8 @@
+using LiteCqrs;
+using TeleWave.Application.Common.Models;
+
+namespace TeleWave.Application.Admin.Users.CreateUser;
+
+/// <summary>Создание пользователя администратором (в обход открытой регистрации), с выбором роли.</summary>
+public sealed record CreateUserCommand(string UserName, string Password, Guid RoleId)
+    : ICommand<Result<Guid>>;