feat: Provisionner automatiquement un nouvel établissement

Lorsqu'un super-admin crée un établissement via l'interface, le système
doit automatiquement créer la base tenant, exécuter les migrations,
créer le premier utilisateur admin et envoyer l'invitation — le tout
de manière asynchrone pour ne pas bloquer la réponse HTTP.

Ce mécanisme rend chaque établissement opérationnel dès sa création
sans intervention manuelle sur l'infrastructure.

backend/tests/Unit/SuperAdmin/Infrastructure/Provisioning/DatabaseTenantProvisionerTest.php

@@ -0,0 +1,72 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\SuperAdmin\Infrastructure\Provisioning;
+
+use App\SuperAdmin\Application\Port\TenantProvisioner;
+use App\SuperAdmin\Infrastructure\Provisioning\DatabaseTenantProvisioner;
+use App\SuperAdmin\Infrastructure\Provisioning\TenantDatabaseCreator;
+use App\SuperAdmin\Infrastructure\Provisioning\TenantMigrator;
+use Doctrine\DBAL\Connection;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\NullLogger;
+use RuntimeException;
+
+final class DatabaseTenantProvisionerTest extends TestCase
+{
+    #[Test]
+    public function itCallsCreatorThenMigratorInOrder(): void
+    {
+        $steps = [];
+
+        $connection = $this->createMock(Connection::class);
+        $connection->method('fetchOne')->willReturn(false);
+        $connection->method('executeStatement')->willReturnCallback(
+            static function () use (&$steps): int {
+                $steps[] = 'create';
+
+                return 1;
+            },
+        );
+
+        $creator = new TenantDatabaseCreator($connection, new NullLogger());
+
+        // TenantMigrator is final — we wrap via the TenantProvisioner interface
+        // to verify the creator is called. Migration subprocess cannot be tested unitarily.
+        $provisioner = new class($creator, $steps) implements TenantProvisioner {
+            /** @param string[] $steps */
+            public function __construct(
+                private readonly TenantDatabaseCreator $creator,
+                private array &$steps,
+            ) {
+            }
+
+            public function provision(string $databaseName): void
+            {
+                $this->creator->create($databaseName);
+                $this->steps[] = 'migrate';
+            }
+        };
+
+        $provisioner->provision('classeo_tenant_test');
+
+        self::assertSame(['create', 'migrate'], $steps);
+    }
+
+    #[Test]
+    public function itPropagatesCreationFailure(): void
+    {
+        $connection = $this->createMock(Connection::class);
+        $connection->method('fetchOne')->willThrowException(new RuntimeException('Connection refused'));
+
+        $creator = new TenantDatabaseCreator($connection, new NullLogger());
+        $migrator = new TenantMigrator('/tmp', 'postgresql://u:p@h/db', new NullLogger());
+
+        $provisioner = new DatabaseTenantProvisioner($creator, $migrator);
+
+        $this->expectException(RuntimeException::class);
+        $provisioner->provision('classeo_tenant_test');
+    }
+}