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/Services/EmailDispatcher.cs

@@ -0,0 +1,73 @@
+using Infrastructure.Email;
+using Infrastructure.Email.Templates.Rendering;
+
+namespace Features.Emails.Services;
+
+/// <summary>
+/// Default implementation of <see cref="IEmailDispatcher"/> that renders email templates and dispatches
+/// them via an <see cref="IEmailProvider"/>.
+/// </summary>
+/// <param name="emailProvider">Provider used to deliver the rendered emails.</param>
+/// <param name="emailTemplateProvider">Provider used to render HTML email bodies from templates.</param>
+public class EmailDispatcher(
+    IEmailProvider emailProvider,
+    IEmailTemplateProvider emailTemplateProvider
+) : IEmailDispatcher
+{
+    /// <summary>
+    /// The base URL of the website, used to build confirmation links. Read from the
+    /// <c>WEBSITE_BASE_URL</c> environment variable.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">
+    /// Thrown at type initialization time when the <c>WEBSITE_BASE_URL</c> environment variable is not set.
+    /// </exception>
+    private static readonly string WebsiteBaseUrl =
+        Environment.GetEnvironmentVariable("WEBSITE_BASE_URL")
+        ?? throw new InvalidOperationException("WEBSITE_BASE_URL environment variable is not set");
+
+    /// <summary>
+    /// Builds a confirmation link from the given token, renders the registration welcome email template,
+    /// and sends it to the newly created user.
+    /// </summary>
+    public async Task SendRegistrationEmailAsync(string firstName, string email, string confirmationToken)
+    {
+        var confirmationLink =
+            $"{WebsiteBaseUrl}/users/confirm?token={confirmationToken}";
+
+        var emailHtml =
+            await emailTemplateProvider.RenderUserRegisteredEmailAsync(
+                firstName,
+                confirmationLink
+            );
+
+        await emailProvider.SendAsync(
+            email,
+            "Welcome to The Biergarten App!",
+            emailHtml,
+            isHtml: true
+        );
+    }
+
+    /// <summary>
+    /// Builds a confirmation link from the given token, renders the resend-confirmation email template,
+    /// and sends it to the user.
+    /// </summary>
+    public async Task SendResendConfirmationEmailAsync(string firstName, string email, string confirmationToken)
+    {
+        var confirmationLink =
+            $"{WebsiteBaseUrl}/users/confirm?token={confirmationToken}";
+
+        var emailHtml =
+            await emailTemplateProvider.RenderResendConfirmationEmailAsync(
+                firstName,
+                confirmationLink
+            );
+
+        await emailProvider.SendAsync(
+            email,
+            "Confirm Your Email - The Biergarten App",
+            emailHtml,
+            isHtml: true
+        );
+    }
+}

web/backend/Features/Features.Emails/Services/IEmailDispatcher.cs

@@ -0,0 +1,25 @@
+namespace Features.Emails.Services;
+
+/// <summary>
+/// Defines operations for sending account-related emails, such as registration and confirmation resend emails.
+/// </summary>
+public interface IEmailDispatcher
+{
+    /// <summary>
+    /// Sends a welcome email containing an account confirmation link to a newly registered user.
+    /// </summary>
+    /// <param name="firstName">The recipient's first name, used to personalize the email.</param>
+    /// <param name="email">The recipient's email address.</param>
+    /// <param name="confirmationToken">The confirmation token to embed in the confirmation link.</param>
+    /// <returns>A task that completes once the email has been sent.</returns>
+    Task SendRegistrationEmailAsync(string firstName, string email, string confirmationToken);
+
+    /// <summary>
+    /// Sends an email containing a fresh account confirmation link to a user who requested a resend.
+    /// </summary>
+    /// <param name="firstName">The recipient's first name, used to personalize the email.</param>
+    /// <param name="email">The recipient's email address.</param>
+    /// <param name="confirmationToken">The confirmation token to embed in the confirmation link.</param>
+    /// <returns>A task that completes once the email has been sent.</returns>
+    Task SendResendConfirmationEmailAsync(string firstName, string email, string confirmationToken);
+}