feat: add comprehensive error handling and logging for vault settings save operations with permission error detection and detailed error messages in UI toast notifications

backend/vault_settings.py

@@ -46,14 +46,27 @@ def save_vault_settings() -> None:
     """Persist vault settings to disk."""
     with _settings_lock:
         try:
+            logger.info(f"Attempting to save settings to {_SETTINGS_PATH}")
+            logger.info(f"Parent directory: {_SETTINGS_PATH.parent}")
+            logger.info(f"Parent exists: {_SETTINGS_PATH.parent.exists()}")
+            
             _SETTINGS_PATH.parent.mkdir(parents=True, exist_ok=True)
-            _SETTINGS_PATH.write_text(
-                json.dumps(_vault_settings, indent=2, ensure_ascii=False),
-                encoding="utf-8"
-            )
-            logger.info(f"Saved settings for {len(_vault_settings)} vaults")
+            logger.info(f"Directory created/verified: {_SETTINGS_PATH.parent}")
+            
+            content = json.dumps(_vault_settings, indent=2, ensure_ascii=False)
+            logger.info(f"JSON content prepared ({len(content)} bytes)")
+            
+            _SETTINGS_PATH.write_text(content, encoding="utf-8")
+            logger.info(f"Successfully saved settings for {len(_vault_settings)} vaults to {_SETTINGS_PATH}")
+        except PermissionError as e:
+            logger.error(f"Permission denied writing to {_SETTINGS_PATH}: {e}")
+            logger.error(f"Check that user has write permissions to {_SETTINGS_PATH.parent}")
+            raise
         except Exception as e:
-            logger.error(f"Failed to save vault settings: {e}")
+            logger.error(f"Failed to save vault settings to {_SETTINGS_PATH}: {e}")
+            logger.error(f"Error type: {type(e).__name__}")
+            import traceback
+            logger.error(f"Traceback: {traceback.format_exc()}")
             raise