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/config/packages/monolog.yaml

@@ -0,0 +1,57 @@
+monolog:
+    channels:
+        - deprecation
+        - security
+        - audit
+
+when@dev:
+    monolog:
+        handlers:
+            main:
+                type: stream
+                path: "%kernel.logs_dir%/%kernel.environment%.log"
+                level: debug
+                channels: ["!event"]
+                formatter: monolog.formatter.json
+            console:
+                type: console
+                process_psr_3_messages: false
+                channels: ["!event", "!doctrine", "!console"]
+
+when@test:
+    monolog:
+        handlers:
+            main:
+                type: fingers_crossed
+                action_level: error
+                handler: nested
+                excluded_http_codes: [404, 405]
+                channels: ["!event"]
+            nested:
+                type: stream
+                path: "%kernel.logs_dir%/%kernel.environment%.log"
+                level: debug
+
+when@prod:
+    monolog:
+        handlers:
+            main:
+                type: fingers_crossed
+                action_level: error
+                handler: nested
+                excluded_http_codes: [404, 405]
+                buffer_size: 50
+            nested:
+                type: stream
+                path: php://stderr
+                level: debug
+                formatter: monolog.formatter.json
+            console:
+                type: console
+                process_psr_3_messages: false
+                channels: ["!event", "!doctrine"]
+            deprecation:
+                type: stream
+                channels: [deprecation]
+                path: php://stderr
+                formatter: monolog.formatter.json