feat: revamp sensor add flow

lib/data/repositories/sensor_repository.dart

@@ -1,6 +1,7 @@
 import '../../domain/models/sensor.dart';
 
 abstract class SensorRepository {
+  Future<Sensor> createSensor(String sensorId, {String? name});
   Future<List<Sensor>> getSensors();
   Future<List<Sensor>> getUnplacedSensors();
   Future<Sensor> getSensor(int id);
@@ -9,4 +10,8 @@ abstract class SensorRepository {
   Future<Sensor> placeSensor(int id,
       {required int roomId, required double x, required double y});
   Future<Sensor> unplaceSensor(int id);
+
+  /// Stream of raw SensorsChannel messages. Each map contains an `event` key
+  /// (`sensor_announced` or `sensor_enrollment_timeout`) plus the payload.
+  Stream<Map<String, dynamic>> sensorEvents();
 }