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/Application/Command/CreateEstablishment/CreateEstablishmentHandlerTest.php

@@ -37,7 +37,7 @@ final class CreateEstablishmentHandlerTest extends TestCase
     }
 
     #[Test]
-    public function createsEstablishmentAndReturnsResult(): void
+    public function createsEstablishmentAndReturnsIt(): void
     {
         $command = new CreateEstablishmentCommand(
             name: 'École Alpha',
@@ -46,13 +46,13 @@ final class CreateEstablishmentHandlerTest extends TestCase
             superAdminId: self::SUPER_ADMIN_ID,
         );
 
-        $result = ($this->handler)($command);
+        $establishment = ($this->handler)($command);
 
-        self::assertNotEmpty($result->establishmentId);
-        self::assertNotEmpty($result->tenantId);
-        self::assertSame('École Alpha', $result->name);
-        self::assertSame('ecole-alpha', $result->subdomain);
-        self::assertStringStartsWith('classeo_tenant_', $result->databaseName);
+        self::assertNotEmpty((string) $establishment->id);
+        self::assertNotEmpty((string) $establishment->tenantId);
+        self::assertSame('École Alpha', $establishment->name);
+        self::assertSame('ecole-alpha', $establishment->subdomain);
+        self::assertStringStartsWith('classeo_tenant_', $establishment->databaseName);
     }
 
     #[Test]
@@ -65,10 +65,10 @@ final class CreateEstablishmentHandlerTest extends TestCase
             superAdminId: self::SUPER_ADMIN_ID,
         );
 
-        $result = ($this->handler)($command);
+        $establishment = ($this->handler)($command);
 
         $establishments = $this->repository->findAll();
         self::assertCount(1, $establishments);
-        self::assertSame($result->establishmentId, (string) $establishments[0]->id);
+        self::assertSame((string) $establishment->id, (string) $establishments[0]->id);
     }
 }