fix: monter PHPStan à niveau 8 — corriger 2 bugs file_get_contents/json_encode

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/Service/Ingestion/IngestionService.php

@@ -188,7 +188,11 @@ class IngestionService
             return null;
         }
 
-        $data = json_decode(file_get_contents($geojsonPath), true);
+        $contents = file_get_contents($geojsonPath);
+        if ($contents === false) {
+            return null;
+        }
+        $data = json_decode($contents, true);
 
         if (empty($data['features'])) {
             return null;

backend/src/Service/Push/PushNotificationService.php

@@ -45,7 +45,7 @@ class PushNotificationService
             'body'    => sprintf('Score %d/100 — %s. Vérifiez avant de partir.', $score, ucfirst($level)),
             'url'     => $this->appPublicUrl,
             'spotId'  => (string) $spot->getId(),
-        ]);
+        ]) ?: null;
 
         $expired = [];