fix(avatar) : address review findings — security and UX fixes

- Use getMimeType() instead of getClientMimeType() to prevent MIME spoofing
- Change IsGranted to IS_AUTHENTICATED_FULLY so ROLE_CLIENT can access avatars
- Remove Groups from avatarFileName (only avatarUrl needed by frontend)
- Disable aggressive caching to prevent stale avatar images
- Add error handling to avatar upload in profile page
- Use i18n for "Mon profil" button text

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

src/Controller/UserAvatarController.php

@@ -30,7 +30,7 @@ class UserAvatarController extends AbstractController
     ) {}
 
     #[Route('/api/users/{id}/avatar', name: 'user_avatar_upload', methods: ['POST'], priority: 1)]
-    #[IsGranted('ROLE_USER')]
+    #[IsGranted('IS_AUTHENTICATED_FULLY')]
     public function upload(int $id, Request $request): JsonResponse
     {
         $user = $this->findUserOrFail($id);
@@ -46,7 +46,7 @@ class UserAvatarController extends AbstractController
             throw new BadRequestHttpException('File size exceeds 5 MB limit.');
         }
 
-        $mimeType = $file->getClientMimeType();
+        $mimeType = $file->getMimeType();
 
         if (!in_array($mimeType, self::ALLOWED_MIME_TYPES, true)) {
             throw new BadRequestHttpException('Invalid file type. Allowed: JPEG, PNG, WebP, GIF.');
@@ -71,7 +71,7 @@ class UserAvatarController extends AbstractController
     }
 
     #[Route('/api/users/{id}/avatar', name: 'user_avatar_serve', methods: ['GET'], priority: 1)]
-    #[IsGranted('ROLE_USER')]
+    #[IsGranted('IS_AUTHENTICATED_FULLY')]
     public function serve(int $id): BinaryFileResponse
     {
         $user = $this->findUserOrFail($id);
@@ -91,13 +91,13 @@ class UserAvatarController extends AbstractController
         $extension = pathinfo($user->getAvatarFileName(), PATHINFO_EXTENSION);
         $mimeMap   = ['jpg' => 'image/jpeg', 'jpeg' => 'image/jpeg', 'png' => 'image/png', 'webp' => 'image/webp', 'gif' => 'image/gif'];
         $response->headers->set('Content-Type', $mimeMap[$extension] ?? 'application/octet-stream');
-        $response->headers->set('Cache-Control', 'public, max-age=86400');
+        $response->headers->set('Cache-Control', 'no-cache, must-revalidate');
 
         return $response;
     }
 
     #[Route('/api/users/{id}/avatar', name: 'user_avatar_delete', methods: ['DELETE'], priority: 1)]
-    #[IsGranted('ROLE_USER')]
+    #[IsGranted('IS_AUTHENTICATED_FULLY')]
     public function delete(int $id): Response
     {
         $user = $this->findUserOrFail($id);