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/RegisterUser/RegisterUserHandler.cs

@@ -0,0 +1,86 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Repository;
+using Features.Auth.Services;
+using Infrastructure.PasswordHashing;
+using MediatR;
+using Shared.Application.Emails;
+
+namespace Features.Auth.Commands.RegisterUser;
+
+/// <summary>
+/// Handles <see cref="RegisterUserCommand"/>: validates uniqueness, hashes the password, persists the
+/// account, issues access/refresh/confirmation tokens, and attempts to send the registration
+/// confirmation email via Features.Emails.
+/// </summary>
+/// <param name="authRepo">Repository used to check for existing users and persist the new account.</param>
+/// <param name="passwordInfrastructure">Infrastructure component used to hash the user's plain-text password.</param>
+/// <param name="tokenService">Service used to generate access, refresh, and confirmation tokens.</param>
+/// <param name="mediator">Used to send the cross-slice command that triggers the confirmation email.</param>
+public class RegisterUserHandler(
+    IAuthRepository authRepo,
+    IPasswordInfrastructure passwordInfrastructure,
+    ITokenService tokenService,
+    IMediator mediator
+) : IRequestHandler<RegisterUserCommand, RegistrationPayload>
+{
+    /// <exception cref="ConflictException">
+    /// Thrown when an existing account already has the same username or email address.
+    /// </exception>
+    public async Task<RegistrationPayload> Handle(RegisterUserCommand request, CancellationToken cancellationToken)
+    {
+        await ValidateUserDoesNotExist(request.Username, request.Email);
+
+        var hashed = passwordInfrastructure.Hash(request.Password);
+
+        var createdUser = await authRepo.RegisterUserAsync(
+            request.Username,
+            request.FirstName,
+            request.LastName,
+            request.Email,
+            request.DateOfBirth,
+            hashed
+        );
+
+        var accessToken = tokenService.GenerateAccessToken(createdUser);
+        var refreshToken = tokenService.GenerateRefreshToken(createdUser);
+        var confirmationToken = tokenService.GenerateConfirmationToken(createdUser);
+
+        if (string.IsNullOrEmpty(accessToken) || string.IsNullOrEmpty(refreshToken))
+        {
+            return new RegistrationPayload(createdUser.UserAccountId, createdUser.Username, string.Empty, string.Empty, false);
+        }
+
+        var emailSent = false;
+        try
+        {
+            await mediator.Send(
+                new SendRegistrationEmailCommand(createdUser.FirstName, createdUser.Email, confirmationToken),
+                cancellationToken
+            );
+            emailSent = true;
+        }
+        catch (Exception ex)
+        {
+            await Console.Error.WriteLineAsync(ex.Message);
+            Console.WriteLine("Could not send email.");
+            // ignored
+        }
+
+        return new RegistrationPayload(createdUser.UserAccountId, createdUser.Username, refreshToken, accessToken, emailSent);
+    }
+
+    /// <exception cref="ConflictException">
+    /// Thrown when an existing account already has the same username or email address.
+    /// </exception>
+    private async Task ValidateUserDoesNotExist(string username, string email)
+    {
+        var existingUsername = await authRepo.GetUserByUsernameAsync(username);
+        var existingEmail = await authRepo.GetUserByEmailAsync(email);
+
+        if (existingUsername != null || existingEmail != null)
+        {
+            throw new ConflictException("Username or email already exists");
+        }
+    }
+}