fix: return to sensors list after cancelling reposition only if you've arrived from there

lib/providers.dart

@@ -166,6 +166,10 @@ final tagProvider =
 /// center-dot placement flow. Cleared on Place, Cancel, or back navigation.
 final sensorPlacementProvider = StateProvider<Sensor?>((ref) => null);
 
+/// True when placement mode was initiated from the sensors list tab.
+/// Used by FloorPlanScreen to decide whether to navigate back on cancel.
+final sensorPlacementOriginSensorsProvider = StateProvider<bool>((ref) => false);
+
 final floorPlanModeProvider =
     StateProvider<FloorPlanMode>((ref) => FloorPlanMode.view);