feat: Implement persistent vault-specific settings management, including loading, saving, and updating preferences.

backend/vault_settings.py

@@ -18,7 +18,7 @@ logger = logging.getLogger("obsigate.vault_settings")
 
 _BASE_DIR = Path(__file__).resolve().parent.parent
 _SETTINGS_PATH = _BASE_DIR / "data" / "vault_settings.json"
-_settings_lock = threading.Lock()
+_settings_lock = threading.RLock()
 
 # In-memory cache of vault settings
 _vault_settings: Dict[str, Dict[str, Any]] = {}