fix: race condition in os.makedirs causing worker crashes

Replace check-then-create pattern with exist_ok=True to prevent
FileExistsError when multiple workers initialize simultaneously.

Affects:
- subscriptions.py: open_database()
- watch.py: save_decrypt_cache()
- local_playlist.py: add_to_playlist()
- util.py: fetch_url(), get_visitor_data()
- settings.py: initialization

Fixes Gunicorn worker startup failures in multi-worker deployments.

youtube/local_playlist.py

@@ -26,8 +26,7 @@ def video_ids_in_playlist(name):
 
 
 def add_to_playlist(name, video_info_list):
-    if not os.path.exists(playlists_directory):
-        os.makedirs(playlists_directory)
+    os.makedirs(playlists_directory, exist_ok=True)
     ids = video_ids_in_playlist(name)
     missing_thumbnails = []
     with open(os.path.join(playlists_directory, name + ".txt"), "a", encoding='utf-8') as file: