fix: Fix logging error in signals endpoint

Fix logger call to use proper string formatting instead of keyword arguments

src/dashboard/api.py

@@ -802,7 +802,7 @@ async def get_signals():
                     signals.extend(_create_fallback_signals(station_id, pump['pump_id']))
                     
     except Exception as e:
-        logger.error(f"error_using_real_protocol_data_using_fallback", error=str(e))
+        logger.error(f"error_using_real_protocol_data_using_fallback: {str(e)}")
         # Fallback to mock data if any error occurs
         for station_id, station in stations.items():
             pumps = pumps_by_station.get(station_id, [])