fix: use created_at_timestamp for Android notification dates; bump to 1.8.3

src/Controllers/ApiController.php

@@ -701,6 +701,7 @@ class ApiController
 
         $data = array_map(function ($n) {
             $n['time_ago'] = time_ago($n['created_at'] ?? '');
+            $n['created_at_timestamp'] = $n['created_at'] ? strtotime($n['created_at']) : 0;
             return $n;
         }, $result['data']);