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/.php-cs-fixer.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+$finder = (new PhpCsFixer\Finder())
+    ->in(__DIR__)
+    ->exclude('var')
+    ->exclude('vendor')
+    // Fichiers auto-générés par Symfony/Doctrine
+    ->notPath('config/bundles.php')
+    ->notPath('config/preload.php')
+    ->notPath('config/reference.php')
+    ->notPath('src/DataFixtures/AppFixtures.php')
+    // Exclusions spécifiques
+    ->notPath('src/Shared/Domain/AggregateRoot.php')
+    ->notPath('src/Shared/Domain/EntityId.php')
+;
+
+return (new PhpCsFixer\Config())
+    ->setRules([
+        '@Symfony' => true,
+        '@Symfony:risky' => true,
+        'declare_strict_types' => true,
+        'strict_param' => true,
+        'array_syntax' => ['syntax' => 'short'],
+        'ordered_imports' => ['sort_algorithm' => 'alpha'],
+        'no_unused_imports' => true,
+        'not_operator_with_successor_space' => true,
+        'trailing_comma_in_multiline' => true,
+        'phpdoc_order' => true,
+        'phpdoc_separation' => true,
+        'phpdoc_no_empty_return' => true,
+        'native_function_invocation' => [
+            'include' => ['@compiler_optimized'],
+            'scope' => 'namespaced',
+            'strict' => true,
+        ],
+        'native_constant_invocation' => true,
+        'global_namespace_import' => [
+            'import_classes' => true,
+            'import_constants' => true,
+            'import_functions' => true,
+        ],
+        'final_class' => true,
+        'class_definition' => [
+            'single_line' => true,
+        ],
+        'concat_space' => [
+            'spacing' => 'one',
+        ],
+        'single_line_throw' => false,
+        // NO Yoda conditions
+        'yoda_style' => false,
+        'blank_line_before_statement' => [
+            'statements' => ['return', 'throw', 'try'],
+        ],
+    ])
+    ->setRiskyAllowed(true)
+    ->setFinder($finder)
+;