Migrate Auth and Emails to vertical slices (Features.Auth, Features.Emails)

Auth and Emails land together since Auth's registration/resend flows need
Emails to exist first. Service.Auth's four services (Register, Login,
Confirmation, Token) collapse into MediatR commands/queries in
Features.Auth; TokenService stays as a slice-internal service since
multiple handlers call it. Auth no longer references Emails directly —
it sends SendRegistrationEmailCommand/SendResendConfirmationEmailCommand
(defined in Shared.Application) which Features.Emails handles, so neither
slice has a project reference on the other.

Service.Emails' IEmailService becomes Features.Emails' IEmailDispatcher,
simplified to take (firstName, email, token) instead of a full UserAccount
since that's all it ever used. API.Specs' TestApiFactory/MockEmailService
are updated to swap in the relocated interface.

Also deletes Infrastructure.Repository now that Breweries, UserManagement,
and Auth have all moved their repos out of it, and replaces the two
now-dead docker-compose test services (repository.tests, service.auth.tests,
both pointing at deleted Dockerfiles) with a single unit.tests service that
runs every Features.*.Tests project via Dockerfile.tests.

web/backend/Features/Features.Emails.Tests/Commands/SendRegistrationEmailHandlerTests.cs

@@ -0,0 +1,24 @@
+using Features.Emails.Commands.SendRegistrationEmail;
+using Features.Emails.Services;
+using Moq;
+using Shared.Application.Emails;
+
+namespace Features.Emails.Tests.Commands;
+
+public class SendRegistrationEmailHandlerTests
+{
+    [Fact]
+    public async Task Handle_DelegatesToEmailDispatcher()
+    {
+        var dispatcherMock = new Mock<IEmailDispatcher>();
+        var handler = new SendRegistrationEmailHandler(dispatcherMock.Object);
+        var command = new SendRegistrationEmailCommand("Aaron", "aaron@example.com", "token-123");
+
+        await handler.Handle(command, CancellationToken.None);
+
+        dispatcherMock.Verify(
+            d => d.SendRegistrationEmailAsync("Aaron", "aaron@example.com", "token-123"),
+            Times.Once
+        );
+    }
+}