feat: Setup projet Classeo avec infrastructure Docker et architecture DDD

Configure l'environnement de développement complet avec Docker Compose,
structure DDD 4 Bounded Contexts, et pipeline CI/CD GitHub Actions.

Corrections compatibilité CI:
- Symfony 8 nécessite monolog-bundle ^4.0 (la v3.x ne supporte que jusqu'à Symfony 7)
- ESLint v9 nécessite flat config (eslint.config.js) - le format .eslintrc.cjs est obsolète

backend/tests/Unit/Shared/Domain/CorrelationIdTest.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Shared\Domain;
+
+use App\Shared\Domain\CorrelationId;
+use PHPUnit\Framework\TestCase;
+use Ramsey\Uuid\Uuid;
+
+final class CorrelationIdTest extends TestCase
+{
+    public function testGenerateCreatesValidUuid(): void
+    {
+        $correlationId = CorrelationId::generate();
+
+        $this->assertTrue(Uuid::isValid($correlationId->value()));
+    }
+
+    public function testFromStringCreatesCorrelationIdFromValidUuid(): void
+    {
+        $uuid = '550e8400-e29b-41d4-a716-446655440000';
+        $correlationId = CorrelationId::fromString($uuid);
+
+        $this->assertSame($uuid, $correlationId->value());
+    }
+
+    public function testValueReturnsUuidString(): void
+    {
+        $uuid = '550e8400-e29b-41d4-a716-446655440000';
+        $correlationId = CorrelationId::fromString($uuid);
+
+        $this->assertSame($uuid, $correlationId->value());
+    }
+
+    public function testToStringReturnsUuidString(): void
+    {
+        $uuid = '550e8400-e29b-41d4-a716-446655440000';
+        $correlationId = CorrelationId::fromString($uuid);
+
+        $this->assertSame($uuid, (string) $correlationId);
+    }
+
+    public function testGenerateCreatesDifferentIdsEachTime(): void
+    {
+        $id1 = CorrelationId::generate();
+        $id2 = CorrelationId::generate();
+
+        $this->assertNotSame($id1->value(), $id2->value());
+    }
+}