feat: Gestion des matières scolaires

Les établissements ont besoin de définir leur référentiel de matières
pour pouvoir ensuite les associer aux enseignants et aux classes.
Cette fonctionnalité permet aux administrateurs de créer, modifier et
archiver les matières avec leurs propriétés (nom, code court, couleur).

L'architecture suit le pattern DDD avec des Value Objects utilisant
les property hooks PHP 8.5 pour garantir l'immutabilité et la validation.
L'isolation multi-tenant est assurée par vérification dans les handlers.

backend/src/Administration/Infrastructure/Persistence/InMemory/InMemorySubjectRepository.php

@@ -0,0 +1,120 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Administration\Infrastructure\Persistence\InMemory;
+
+use App\Administration\Domain\Exception\SubjectNotFoundException;
+use App\Administration\Domain\Model\SchoolClass\SchoolId;
+use App\Administration\Domain\Model\Subject\Subject;
+use App\Administration\Domain\Model\Subject\SubjectCode;
+use App\Administration\Domain\Model\Subject\SubjectId;
+use App\Administration\Domain\Model\Subject\SubjectStatus;
+use App\Administration\Domain\Repository\SubjectRepository;
+use App\Shared\Domain\Tenant\TenantId;
+
+use function mb_strtolower;
+
+use Override;
+
+final class InMemorySubjectRepository implements SubjectRepository
+{
+    /** @var array<string, Subject> Indexed by ID */
+    private array $byId = [];
+
+    /** @var array<string, Subject> Indexed by tenant:school:code */
+    private array $byTenantSchoolCode = [];
+
+    /** @var array<string, string> Maps subject ID to its current code key */
+    private array $codeKeyById = [];
+
+    #[Override]
+    public function save(Subject $subject): void
+    {
+        $subjectIdStr = (string) $subject->id;
+
+        // If subject already exists, remove the old code key (handles code changes)
+        if (isset($this->codeKeyById[$subjectIdStr])) {
+            $oldKey = $this->codeKeyById[$subjectIdStr];
+            unset($this->byTenantSchoolCode[$oldKey]);
+        }
+
+        $newKey = $this->codeKey($subject->code, $subject->tenantId, $subject->schoolId);
+
+        $this->byId[$subjectIdStr] = $subject;
+        $this->byTenantSchoolCode[$newKey] = $subject;
+        $this->codeKeyById[$subjectIdStr] = $newKey;
+    }
+
+    #[Override]
+    public function get(SubjectId $id): Subject
+    {
+        $subject = $this->findById($id);
+
+        if ($subject === null) {
+            throw SubjectNotFoundException::withId($id);
+        }
+
+        return $subject;
+    }
+
+    #[Override]
+    public function findById(SubjectId $id): ?Subject
+    {
+        return $this->byId[(string) $id] ?? null;
+    }
+
+    #[Override]
+    public function findByCode(
+        SubjectCode $code,
+        TenantId $tenantId,
+        SchoolId $schoolId,
+    ): ?Subject {
+        $subject = $this->byTenantSchoolCode[$this->codeKey($code, $tenantId, $schoolId)] ?? null;
+
+        // Filtrer les matières archivées (comme Doctrine avec deleted_at IS NULL)
+        if ($subject !== null && $subject->deletedAt !== null) {
+            return null;
+        }
+
+        return $subject;
+    }
+
+    #[Override]
+    public function findActiveByTenantAndSchool(
+        TenantId $tenantId,
+        SchoolId $schoolId,
+    ): array {
+        $result = [];
+
+        foreach ($this->byId as $subject) {
+            if ($subject->tenantId->equals($tenantId)
+                && $subject->schoolId->equals($schoolId)
+                && $subject->status === SubjectStatus::ACTIVE
+            ) {
+                $result[] = $subject;
+            }
+        }
+
+        return $result;
+    }
+
+    #[Override]
+    public function delete(SubjectId $id): void
+    {
+        $subjectIdStr = (string) $id;
+
+        if (isset($this->byId[$subjectIdStr])) {
+            if (isset($this->codeKeyById[$subjectIdStr])) {
+                unset($this->byTenantSchoolCode[$this->codeKeyById[$subjectIdStr]]);
+                unset($this->codeKeyById[$subjectIdStr]);
+            }
+            unset($this->byId[$subjectIdStr]);
+        }
+    }
+
+    private function codeKey(SubjectCode $code, TenantId $tenantId, SchoolId $schoolId): string
+    {
+        return $tenantId . ':' . $schoolId . ':' . mb_strtolower((string) $code, 'UTF-8');
+    }
+}