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/Scolarite/Infrastructure/Storage/S3FileStorageTest.php

@@ -0,0 +1,141 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Scolarite\Infrastructure\Storage;
+
+use App\Scolarite\Infrastructure\Storage\S3FileStorage;
+
+use function fopen;
+
+use League\Flysystem\Filesystem;
+use League\Flysystem\UnableToDeleteFile;
+use League\Flysystem\UnableToReadFile;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+use ReflectionClass;
+use RuntimeException;
+
+final class S3FileStorageTest extends TestCase
+{
+    private Filesystem $filesystem;
+    private LoggerInterface $logger;
+    private S3FileStorage $storage;
+
+    protected function setUp(): void
+    {
+        $this->filesystem = $this->createMock(Filesystem::class);
+        $this->logger = $this->createMock(LoggerInterface::class);
+
+        $this->storage = $this->createStorageWithMockedFilesystem($this->filesystem, $this->logger);
+    }
+
+    #[Test]
+    public function uploadWritesStringContentToFilesystem(): void
+    {
+        $this->filesystem->expects(self::once())
+            ->method('write')
+            ->with('homework/abc/file.pdf', 'fake content', ['ContentType' => 'application/pdf']);
+
+        $result = $this->storage->upload('homework/abc/file.pdf', 'fake content', 'application/pdf');
+
+        self::assertSame('homework/abc/file.pdf', $result);
+    }
+
+    #[Test]
+    public function uploadWritesStreamContentToFilesystem(): void
+    {
+        /** @var resource $stream */
+        $stream = fopen('php://memory', 'r+');
+
+        $this->filesystem->expects(self::once())
+            ->method('writeStream')
+            ->with('homework/abc/file.pdf', $stream, ['ContentType' => 'application/pdf']);
+
+        $result = $this->storage->upload('homework/abc/file.pdf', $stream, 'application/pdf');
+
+        self::assertSame('homework/abc/file.pdf', $result);
+    }
+
+    #[Test]
+    public function deleteRemovesFileFromFilesystem(): void
+    {
+        $this->filesystem->expects(self::once())
+            ->method('delete')
+            ->with('homework/abc/file.pdf');
+
+        $this->logger->expects(self::never())
+            ->method('warning');
+
+        $this->storage->delete('homework/abc/file.pdf');
+    }
+
+    #[Test]
+    public function deleteLogsWarningOnFailure(): void
+    {
+        $this->filesystem->expects(self::once())
+            ->method('delete')
+            ->willThrowException(UnableToDeleteFile::atLocation('homework/abc/file.pdf'));
+
+        $this->logger->expects(self::once())
+            ->method('warning')
+            ->with(
+                'S3 delete failed, possible orphan blob: {path}',
+                self::callback(static fn (array $context): bool => $context['path'] === 'homework/abc/file.pdf'),
+            );
+
+        $this->storage->delete('homework/abc/file.pdf');
+    }
+
+    #[Test]
+    public function readStreamReturnsResourceFromFilesystem(): void
+    {
+        /** @var resource $expectedStream */
+        $expectedStream = fopen('php://memory', 'r+');
+
+        $this->filesystem->expects(self::once())
+            ->method('readStream')
+            ->with('homework/abc/file.pdf')
+            ->willReturn($expectedStream);
+
+        $result = $this->storage->readStream('homework/abc/file.pdf');
+
+        self::assertSame($expectedStream, $result);
+    }
+
+    #[Test]
+    public function readStreamThrowsRuntimeExceptionOnMissingFile(): void
+    {
+        $this->filesystem->expects(self::once())
+            ->method('readStream')
+            ->with('homework/abc/missing.pdf')
+            ->willThrowException(UnableToReadFile::fromLocation('homework/abc/missing.pdf'));
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Impossible de lire le fichier : homework/abc/missing.pdf');
+
+        $this->storage->readStream('homework/abc/missing.pdf');
+    }
+
+    /**
+     * Creates an S3FileStorage instance with a mocked Filesystem injected via reflection.
+     *
+     * S3FileStorage is `final readonly` and its constructor creates a real S3Client,
+     * so we bypass it with newInstanceWithoutConstructor() and inject mocks directly.
+     * If the class gains new properties, this method must be updated.
+     */
+    private function createStorageWithMockedFilesystem(Filesystem $filesystem, LoggerInterface $logger): S3FileStorage
+    {
+        $reflection = new ReflectionClass(S3FileStorage::class);
+        $storage = $reflection->newInstanceWithoutConstructor();
+
+        $fsProp = $reflection->getProperty('filesystem');
+        $fsProp->setValue($storage, $filesystem);
+
+        $loggerProp = $reflection->getProperty('logger');
+        $loggerProp->setValue($storage, $logger);
+
+        return $storage;
+    }
+}