fix backend CORS: add global CORS filter and catch-all OPTIONS route; fix MySQL insert errors: set updatedField to empty string instead of null in models without updated_at column

app/Models/CategoryModel.php

@@ -22,7 +22,7 @@ class CategoryModel extends Model
 
     protected $useTimestamps = true;
     protected $createdField = 'created_at';
-    protected $updatedField = null;
+    protected $updatedField = '';
 
     protected $validationRules = [
         'user_id' => 'required',