feat(avatar) : add avatar upload/serve/delete controller

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config/services.yaml

@@ -8,6 +8,7 @@
 # https://symfony.com/doc/current/best_practices.html#use-parameters-for-application-configuration
 parameters:
     task_document_upload_dir: '%kernel.project_dir%/var/uploads/documents'
+    avatar_upload_dir: '%kernel.project_dir%/var/uploads/avatars'
 
 imports:
     - { resource: version.yaml }
@@ -39,3 +40,7 @@ services:
     App\Controller\TaskDocumentDownloadController:
         arguments:
             $uploadDir: '%task_document_upload_dir%'
+
+    App\Controller\UserAvatarController:
+        arguments:
+            $avatarUploadDir: '%avatar_upload_dir%'