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/subscriptions.py

@@ -30,8 +30,7 @@ database_path = os.path.join(settings.data_dir, "subscriptions.sqlite")
 
 
 def open_database():
-    if not os.path.exists(settings.data_dir):
-        os.makedirs(settings.data_dir)
+    os.makedirs(settings.data_dir, exist_ok=True)
     connection = sqlite3.connect(database_path, check_same_thread=False)
 
     try: