Add self-service account management commands (delete, update username/email/password/profile)

web/backend/Features/Features.Auth/Commands/UpdateEmail/UpdateEmailValidator.cs

@@ -0,0 +1,18 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.UpdateEmail;
+
+/// <summary>Validates <see cref="UpdateEmailCommand" />, mirroring the email rules in <c>RegisterUserValidator</c>.</summary>
+public class UpdateEmailValidator : AbstractValidator<UpdateEmailCommand>
+{
+    public UpdateEmailValidator()
+    {
+        RuleFor(x => x.NewEmail)
+            .NotEmpty()
+            .WithMessage("Email is required")
+            .EmailAddress()
+            .WithMessage("Invalid email format")
+            .MaximumLength(128)
+            .WithMessage("Email cannot exceed 128 characters");
+    }
+}