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.Auth/Commands/ConfirmUser/ConfirmUserHandler.cs

@@ -0,0 +1,36 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Repository;
+using Features.Auth.Services;
+using MediatR;
+
+namespace Features.Auth.Commands.ConfirmUser;
+
+/// <summary>
+/// Handles <see cref="ConfirmUserCommand"/> by validating the confirmation token and marking the
+/// corresponding user account as confirmed.
+/// </summary>
+/// <param name="authRepository">Repository used to look up and confirm user accounts.</param>
+/// <param name="tokenService">Service used to validate the confirmation token.</param>
+public class ConfirmUserHandler(
+    IAuthRepository authRepository,
+    ITokenService tokenService
+) : IRequestHandler<ConfirmUserCommand, ConfirmationPayload>
+{
+    /// <exception cref="UnauthorizedException">
+    /// Thrown when the confirmation token is invalid or expired, or when the associated user account cannot be found.
+    /// </exception>
+    public async Task<ConfirmationPayload> Handle(ConfirmUserCommand request, CancellationToken cancellationToken)
+    {
+        var validatedToken = await tokenService.ValidateConfirmationTokenAsync(request.Token);
+
+        var user = await authRepository.ConfirmUserAccountAsync(validatedToken.UserId);
+
+        if (user == null)
+        {
+            throw new UnauthorizedException("User account not found");
+        }
+
+        return new ConfirmationPayload(user.UserAccountId, DateTime.UtcNow);
+    }
+}