start (actual) email auth, add CancellationToken to most async methods

Foxnouns.Backend/Mailables/AccountCreationMailable.cs

@@ -0,0 +1,19 @@
+using Coravel.Mailer.Mail;
+
+namespace Foxnouns.Backend.Mailables;
+
+public class AccountCreationMailable(Config config, AccountCreationMailableView view) : Mailable<AccountCreationMailableView>
+{
+    public override void Build()
+    {
+        To(view.To)
+            .From(config.EmailAuth.From!)
+            .View("~/Views/Mail/AccountCreation.cshtml", view);
+    }
+}
+
+public class AccountCreationMailableView
+{
+    public required string To { get; init; }
+    public required string Code { get; init; }
+}