Update XML doc comment in backend projects

web/backend/Features/Features.Auth/Commands/RefreshToken/RefreshTokenHandler.cs

@@ -11,6 +11,10 @@ namespace Features.Auth.Commands.RefreshToken;
 public class RefreshTokenHandler(ITokenService tokenService)
     : IRequestHandler<RefreshTokenCommand, LoginPayload>
 {
+    /// <exception cref="Domain.Exceptions.UnauthorizedException">
+    ///     Thrown when the refresh token is invalid or expired, or when the user account it refers to no
+    ///     longer exists.
+    /// </exception>
     public async Task<LoginPayload> Handle(
         RefreshTokenCommand request,
         CancellationToken cancellationToken

web/backend/Features/Features.Auth/Commands/RefreshToken/RefreshTokenValidator.cs

@@ -2,6 +2,7 @@ using FluentValidation;
 
 namespace Features.Auth.Commands.RefreshToken;
 
+/// <summary>Validates that <see cref="RefreshTokenCommand.RefreshToken" /> is present.</summary>
 public class RefreshTokenValidator : AbstractValidator<RefreshTokenCommand>
 {
     public RefreshTokenValidator()

web/backend/Features/Features.Auth/Commands/RegisterUser/RegisterUserValidator.cs

@@ -2,6 +2,10 @@ using FluentValidation;
 
 namespace Features.Auth.Commands.RegisterUser;
 
+/// <summary>
+///     Validates the field-level constraints on <see cref="RegisterUserCommand" />: username format and
+///     length, name lengths, email format, minimum age of 19, and password complexity.
+/// </summary>
 public class RegisterUserValidator : AbstractValidator<RegisterUserCommand>
 {
     public RegisterUserValidator()