Add settings endpoints and registration status check: implement new API endpoints for settings management, including registration status retrieval, and update the registration command handler to enforce registration rules based on site settings.

backend/src/TeleWave.Application/Auth/AuthErrors.cs

@@ -26,4 +26,9 @@ public static class AuthErrors
         "Auth.UserNameTaken",
         "Это имя пользователя уже занято."
     );
+
+    public static readonly Error RegistrationDisabled = Error.Forbidden(
+        "Auth.RegistrationDisabled",
+        "Регистрация на сайте отключена администратором."
+    );
 }

backend/src/TeleWave.Application/Auth/Register/RegisterCommandHandler.cs

@@ -7,7 +7,8 @@ namespace TeleWave.Application.Auth.Register;
 public sealed class RegisterCommandHandler(
     IIdentityService identityService,
     IJwtTokenService jwtTokenService,
-    IRefreshTokenService refreshTokenService
+    IRefreshTokenService refreshTokenService,
+    ISiteSettings siteSettings
 ) : ICommandHandler<RegisterCommand, Result<AuthResult>>
 {
     public async Task<Result<AuthResult>> Handle(
@@ -15,6 +16,10 @@ public sealed class RegisterCommandHandler(
         CancellationToken cancellationToken
     )
     {
+        // Открытая регистрация должна быть явно включена админом; иначе учётки заводит только он.
+        if (!await siteSettings.IsRegistrationEnabledAsync(cancellationToken))
+            return Result.Failure<AuthResult>(AuthErrors.RegistrationDisabled);
+
         var createResult = await identityService.CreateUserAsync(
             command.UserName,
             command.Password,