implement auth controller and routes

Wires AuthController (signup, confirmEmail, login, me, logout)
to the existing auth use cases. Routes mounted under /api with
AuthMiddleware on logout/me. RepositoryServiceProvider gains
EmailConfirmationToken and Post bindings; AppServiceProvider
binds the Emailer/EmailFactory and constructs SignupUser with
the configured from-address.

backend/app/Providers/RepositoryServiceProvider.php

@@ -4,6 +4,10 @@ namespace App\Providers;
 
 use App\Auth\EloquentSessionRepository;
 use App\Auth\SessionRepository;
+use App\Email\EmailConfirmationToken\EloquentEmailConfirmationTokenRepository;
+use App\Email\EmailConfirmationToken\EmailConfirmationTokenRepository;
+use App\Post\EloquentPostRepository;
+use App\Post\PostRepository;
 use App\User\EloquentUserRepository;
 use App\User\UserRepository;
 use Illuminate\Support\ServiceProvider;
@@ -20,5 +24,13 @@ class RepositoryServiceProvider extends ServiceProvider
             SessionRepository::class,
             EloquentSessionRepository::class,
         );
+        $this->app->bind(
+            EmailConfirmationTokenRepository::class,
+            EloquentEmailConfirmationTokenRepository::class,
+        );
+        $this->app->bind(
+            PostRepository::class,
+            EloquentPostRepository::class,
+        );
     }
 }