fix: pass data as array not JSON string for JSONB column

The notifications.data column is JSONB. Database::insert() already
json_encodes the full payload, so passing json_encode() double-encodes
it into a string. Mobile app expects a Map, not a string.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/notifications/controller.php

@@ -124,7 +124,7 @@ class NotificationsController
                     'title_ar' => $titleAr,
                     'body' => $bodyAr,
                     'body_ar' => $bodyAr,
-                    'data' => json_encode(['campaign_id' => $campaignId]),
+                    'data' => ['campaign_id' => $campaignId],
                 ];
             }
             $result = $this->db->insert('notifications', $rows);
@@ -237,7 +237,7 @@ class NotificationsController
             'title_ar' => $titleAr,
             'body' => $bodyAr,
             'body_ar' => $bodyAr,
-            'data' => json_encode(['campaign_id' => $campaignId]),
+            'data' => ['campaign_id' => $campaignId],
         ]);
 
         $success = $result && !isset($result['message']);